Advances in Biological Regulation 54 (2014) 231–241

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An aspirin a day Philip W. Majerus Division of Hematology, Washington University, School of Medicine, St. Louis, MO 63110, USA

a b s t r a c t The title of this article is also its punch line. The thesis that I will prove is that every adult, with a few exceptions, should take one 325 mg aspirin tablet each day. The drug is extraordinary and is beneficial in myriad ways. In this dosage the toxicity of the treatment is minimal. Since the drug is sold “over the counter”, not requiring prescription, it is cheap and its benefits are easily underestimated. I do not use extensive reference citations; but just tell the story of aspirin. Ó 2013 Published by Elsevier Ltd.

The beginnings Joseph Lister (1827–1912) has been referred to as the father of modern surgery (Fisher, 1977). He was born to a wealthy quaker family in Suburban London. From his earliest days he was interested in science and experimentation. He attended University College London from 1844 until 1853. Upon completing medical school he obtained a post in Edinburgh with Mr. James Syme, one of the most famous surgeons in Britain. He thrived under Syme and in 1856 he married Syme’s daughter Agnes. Agnes Lister served as Joseph’s assistant for the rest of her life. At this time in the nineteenth century sepsis was rampant in hospitals all over the world resulting in the death of 25–50% of patients with compound fractures (those where bone protruded through the skin). Syme told Lister ”that it would on the whole be better if all compound fractures of the leg were subjected to amputation without any attempt to save the limb” In these times sepsis was more common in hospitalized patients than in those treated elsewhere. It was postulated that something in the setting of a hospital was evil. The causes of sepsis were unknown and often ascribed to vague concepts as “miasmas” or “ethers”. When Lister learned of the work of Louis Pasteur on bacterial fermentation published in 1860 he had a eureka moment. He realized that sepsis was caused by the growth of microorganisms within the wounds of the patients. He quickly adopted the practice of

E-mail address: [email protected]. 2212-4926/$ – see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.jbior.2013.09.011

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soaking the instruments and sponges to be used in surgery in the strong disinfectant phenol. This agent (hydroxyl benzene) is both noxious and toxic to man. The results of this practice were spectacular. There was a marked reduction in wound infections. During this period he also used salicylic acid as a disinfectant. This agent although less potent than phenol was also much less toxic. He postulated that the source of the bacteria causing infections was the air in the operating room. He introduced phenol sprays into the air in the operating room with disastrous results to the surgeons. He then reverted to salicylic acid which was more tolerable. Between 1800 and 1835, chemists in Germany, France and Italy were able to extract salicin from plants and convert it into salicylic acid, and purify it for human consumption (Rainsford, 1984). But in this form it was very harsh on people’s stomachs. A French chemist, Charles Gerhardt, was studying possible ways to buffer salicylic acid in the 1850’s. He neutralized salicylic acid as a sodium salt and added acetyl chloride as a further attempt to buffer. This combination formed a somewhat unstable form of acetylsalicylic acid in 1853 (later known as aspirin). Gerhardt dropped the project as he had no interest in commercializing aspirin. He allegedly offered a sample to Lister to try in place of salicylic acid. Lister declined saying that salicylic acid was satisfactory. Another chemist, Karl Johann Kraut, in 1869 produced aspirin in a more stable form but did nothing with it. Because of this, progress in the study of aspirin was delayed almost 30 years. The story of aspirin was resumed in 1898 when Felix Hoffman, a 29 year old chemist at Bayer, rejuvenated aspirin. He had been directed by his superiors to find a form of salicylic acid that was less toxic to the stomach. His work was more in the library than in the laboratory as he found accounts of the work of Gerhardt and Kraut. He devised a much superior method for making aspirin that involved refluxing acetic anhydride and salicylic together and subsequently extracting the product aspirin into ether (Mann and Plummer, 1991). Hoffman’s father suffered from rheumatoid arthritis and was unable to tolerate high doses of salicylic acid because of stomach upset. He implored his son to find another remedy that might be less toxic. After reviewing the literature describing salicylic acid he came across the work of Gerhardt’s attempt to buffer salicylic acid that led to the formation of aspirin. He then synthesized a sample of aspirin by the above improved method that yielded more pure and more stable aspirin. He gave a sample to his father with excellent results as it was well tolerated. From the time of the treatment of Hoffman’s father until aspirin reached the market was only one year! The directors of the laboratory, Arthur Eichengrun and Henrich Dresser sent samples of aspirin to German physicians in Berlin and encouraged them to try it and to publish their results. They found it to be a potent antipyretic, a pain reliever, and an anti-inflammatory agent useful in the treatment of rheumatic fever and rheumatoid arthritis. Within 3 years some 160 scientific articles appeared extolling the virtues of aspirin. No studies were done to elucidate the mechanism of aspirins efficacy. Some facts were puzzling. Aspirin reduced fever, yet did not reduce body temperature in those who were without fever. Aspirin quickly became an immensely popular drug selling vast quantities. In 1917 Monsanto began to make aspirin in the US and eventually produced all of the aspirin made in the US including that sold by Bayer. Aspirin is now the second most used drug in the world after alcohol. Aspirin is used in widely varying dosages, from 3 to 6 g/day to combat inflammation, and much lower doses to reduce fever and relieve headaches and other musculoskeletal pains. Dosage will become important as we shall see later, as toxicity is highly dose related. Newly discovered uses for aspirin In order to understand the data on the benefits of aspirin, a number of basic concepts need to be understood. The first is the difference between absolute and relative risk. For example consider seat belt use in automobile travel. The relative benefit of seat belt use is clear. Wearing seat belts reduces the risk of fatal motor vehicle accidents by several fold (this is the relative benefit). However, the absolute risk of a fatal auto accident is quite low. Thus one is unlikely to break into a sweat over a short trip to the store without using a seat belt (this reflects the absolute risk). Many therapeutic trials in medical research present data as relative risks only and this is sometimes misleading. If a study reports that a treatment reduces death from 4.5% to 3.5% this reflects a relative reduction of almost 29% which sounds impressive, but the absolute benefit is actually a modest 1%. Also note that these relative data have little meaning to the individual subject. The individual either lives or dies and that is what is meaningful.

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Another concept is the “risk benefit ratio”. If a particular treatment is very toxic the aforementioned 29% benefit might not be worthwhile. For instance if severe toxicity occurs in one forth of subjects perhaps one would chose to opt out. If the toxicity is minimal, one would go for it. A third concept is the difference between randomized control trials (RCT) and observational studies. In an RCT the study population is compared to a randomly selected group of normal subjects. This is intended to minimize bias. In observational studies a population is surveyed for the occurrence of some factor. The original study by the American cancer society questioned over one million subjects about cigarette smoking. They observed that the incidence of lung cancer was more that 10 times higher among smokers compared to nonsmokers. The evidence was strong but perhaps not conclusive. Could there be some confounding factor that is the true cause of lung cancer which also results in increased smoking among cancer victims. For example, what if boredom with life causes lung cancer and also increases smoking behavior? Thus observational studies are an indication of cause but are not by themselves conclusive. However RCT can also be misleading. An example is the observational study of estrogen use among nurses. The nurses health study surveyed over 100,000 nurses over a prolonged period and observed that estrogen use by nurses was associated with a decrease in cardiovascular disease with only minor increases in breast and uterine cancer. A later RCT concluded that estrogen use did not decrease cardiovascular disease but in fact increased it. However there was a big difference between the study populations that may have confounded the results. In the RCT study estrogen use commenced with the initiation of the study and not co-incident with menopause, which was the case in the nurses observational study. In the RCT study some women started estrogen therapy many years after menopause. This could result in many different effects than those obtained with estrogen given only at the time of menopause. So I assert that the risks and benefits of estrogen use remain uncertain. Another type of observational study is a case control study. In this type of study a number of patients with the disease in question are compared to a group who do not have the disease. All are asked about some practice or factor. For example if heart attack is the disease being investigated, all subjects are queried about estrogen use. If estrogen use reduces the frequency of heart attacks, less subjects in that group will report using estrogens. A variation of this type of study is a cohort study. In this case a group of women who use estrogen are compared to a group that do not. If estrogen use is beneficial, then less heart attacks will occur in the estrogen-using group over a period of follow-up. Another concept to understand is that the frequency of an event that is to be prevented has a huge effect on the size and duration of the trial needed in order to achieve a statistically significant result. Therefore rare events require large sample sizes and prolonged durations of study. This means that it is much easier to study common events than rare ones. Finally a bit about the chemistry of aspirin: Aspirin is acetyl salicylic acid and the molecule consists of a union between acetic acid and salicylic acid by splitting out a water molecule. Such compounds where 2 acids are joined by splitting out a water molecule are called anhydrides. Such compounds are very unstable and react spontaneously with other compounds to form stable products (Fig. 1). In this way aspirin is unlike salicylic acid. Although both have anti-inflammatory actions only aspirin is reactive, with the ability to form stabile products and as we shall see later this property forms the basis for its unique actions. It has been clear for years that aspirin has effects on blood coagulation. Early studies were performed by Lawrence Craven, a California ENT specialist. Craven reported that he often prescribed aspergum, a chewable form of aspirin to patients after tonsillectomy to alleviate post-operative pain. Several of his patients bleed badly a few days after the operation. After further questioning, he learned “that in every instance of severe bleeding the patient had not only chewed the four sticks of aspergum per day as ordered but had purchased an additional supply, consuming up to 20 sticks per day, the eqivalent of over 4 g of aspirin”. Craven concluded from these findings that aspirin must decrease the formation of thrombi. If true, he wondered if aspirin might decrease the risk of heart attacks. Based on this reasoning he began to suggest that middle aged men take 2–6 aspirin tablets per day. At one point Craven reported that “more than 400 men have done so and none of these have suffered a coronary thrombosis.” Craven continued to urge patients and friends to take aspirin although he did lower the dose to 1 to 2 tablets per day. By 1953 Craven had put almost 1500 male patients on aspirin. By three years later the number reached 8000. Among those taking aspirin Craven reported that “not a single

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Fig. 1. Chemical reactions for aspirine synthesis.

case of detectable coronary or cerebral thrombosis had occurred among patients who faithfully adhered to this regimen.” He claimed that the nine men who apparently died of coronary thrombosis were found to have ruptured vessels or aneurisms upon autopsy. His results, reported in the obscure Mississippi Valley Medical Journal, were ignored by the scientific community. Upon reflecting upon his results they seem too good to be true. As we shall see in later studies aspirin does decrease thrombosis, but the effect is not absolute as Craven would suggest. Aspirin reduces but does not eliminate heart attacks. How platelets work Studies of the effect of aspirin on various coagulation reactions suggested that the effect of aspirin was not on the clotting process per se. For example aspirin has very little effect on standard assays of coagulation. Aspirin has no effect on the time required for blood to clot in vitro (Weiss et al., 1968). Reports of easy bruising after aspirin use are common, especially in women. It was postulated that aspirin somehow affected platelet function. Blood platelets are small cells of only 2-4 microns in diameter. They have no nuclei and are nearly devoid of the ability to make new proteins. (see Fig. 2) They contain numerous a granules that secrete their contents of clotting factors and growth factors upon activation. They also contain dense granules that contain nucleotides and serotonin. They contain

Fig. 2. Structure of platelets.

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mitochondria and a system of canaliculi that are connected to the surface membrane making the cells have a huge surface area to volume ratio. Platelets are activated to secrete granule contents and to aggregate in response to various stimuli. The most potent factor that activates platelets is the clotting factor thrombin. They are also activated by subendothelial collagen, by adenosine diphosphate (ADP), and by the prostaglandin thromboxane A2. Platelets serve to stop blood loss at sites of vascular injury. Blood vessels are lined by specialized cells called endothelial cells. When a blood vessel is injured disrupting the endothelial layer, platelets bind to the subendothelial collagen and then additional platelets are activated and clump together at the site forming a physical plug that stops blood loss. Subsequently a blood clot forms at the site of clumped platelets, a process that is stimulated by secreted clotting factors. After a clot is formed the platelets consolidate the clot and seal the wound. A number of the factors secreted, especially platelet derived growth factor, contribute to wound healing and the eventual dissolution of the clot. That aspirin interferes with the process is suggested by the bruising history and also by laboratory tests of platelet function. One such test is the measurement of the time of bleeding after making a small skin wound with a needle. When subjects who have used aspirin are tested, the time of bleeding is prolonged from the normal value of 4–7 min –10 min or more. Another common test is platelet aggregation which mimics the platelet plug formation described above. In this test platelets are isolated from blood and then stirred in a tube through which a light is shown. Light transmission through the stirring platelet suspension is measured. Then an agent which activates platelets (such as thrombin) is added, causing the platelets to clump or aggregate. This results in increased light transmission due to the decreased turbidity. When platelets are isolated from subjects who have taken aspirin, aggregation in response to certain platelet activating agents, such as ADP and collagen, is impaired. Thrombin activation of platelets is not impaired by aspirin, which explains why the aspirin bleeding defect is usually mild. What aspirin does The action of aspirin on platelets was worked out by a number of laboratories. John Vane in England studied the production of factors that constrict rabbit aorta strips using a complex bioassay system (Vane, 1971). In these experiments, “factors” were prepared by treating guinea pig lung with various stimuli including arachidonic acid. The solutions from the lung perfusion were then poured onto rabbit aorta strips and the degree of contraction was measured. The substance produced by guinea pig lungs was named RCS, for rabbit aorta contracting substance. Vane found that if the guinea pig lung or extracts from guinea pig lung were treated with aspirin before adding arachidonic acid no RCS was produced. If aspirin was added after arachidonic acid no inhibition of RCS formation occurred. Because of these findings he postulated that RCS was a prostaglandin whose production was blocked by aspirin. Vane was never able to further characterize RCS but later Bengt Samuelson in Sweden showed that RCS was thromboxane A2. Because of Vane results, Smith and Willis studied the formation of prostaglandins in platelets. They showed that aspirin inhibited the synthesis of prostaglandins in platelets in 1971 (Smith and Willis, 1971). Prostaglandins are formed by the enzymatic addition of oxygen atoms to arachidonic acid. Prostaglandins have numerous functions. Some cause fever, others cause inflammation, and one of them causes platelet aggregation. Other derivatives of arachidonic acid are the leukotrienes (see Fig. 3). This leads me to describe experiments done in my laboratory to define the action of aspirin (Roth and Majerus, 1975). Because aspirin is an anhydride of acetic and salicylic acids as outlined earlier, I thought that it should be highly reactive and therefore able to add acetyl groups to other molecules. My postdoctoral fellow Jerry Roth and I synthesized radioactive aspirin with a tritium atom incorporated into either the acetyl group on the salicylic group. Others had attempted to prepare radiolabelled aspirin in an effort to show acetylation but they failed because the amount of radioactivity incorporated was too low do demonstrate any incorporation into either coagulation factors or platelets. In the procedure we developed the volumes of the reactions were only a few micoliters (one ten thousandth of an ounce). By this method it was possible to make aspirin highly radioactive (about 400 radioactive counts per minute per picomole). With this preparation we could detect any incorporation if it occurred. In our initial experiments, Jerry added radioactive aspirin to various coagulation factors and

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Fig. 3. Scheme of prostaglandin and leukotriene products of arachidonic acid.

to human plasma but he saw no incorporation of radioactivity into any protein. At this point I left the lab for a ski vacation and while I was away Jerry tried adding aspirin to blood platelets with spectacular results. When acetyl labeled aspirin was added to platelets, a single membrane protein became labeled with radioactivity. When salicylic labeled aspirin was used, no radioactivity was incorporated into the platelets. This meant that a platelet membrane protein was being acetylated by aspirin. We also showed that the reaction required only tiny amounts of aspirin (the equivalent of about 1/10 th of a tablet) to fully saturate the process (i.e., no more radioactivity could be incorporated even with larger amounts of aspirin). We also showed that the acetylation was permanent lasting for the life of the platelet (about 10 days). We studied the acetylation in another way. We treated ourselves with 640 mg of unlabeled aspirin and then drew blood samples daily, isolated platelets, and added radioactive aspirin in vitro to determine the ability to find any radiolabeled platelets. No radioactive platelets appeared until the third day after oral aspirin indicating that acetylation occurred in the bone marrow precursors of platelets, megakaryocytes. Megakaryocytes are bone marrow cells from which platelets “bud off”. Full acetylation was achieved only after about 14 days when the entire population of our platelets was new. After considerably more work we were able to show that the protein that was being acetylated was an enzyme called cyclooxygenase, which catalyzes the first step in prostaglandin synthesis. We showed that acetylation blocked the binding of the substrate arachidonic acid to the enzyme and thereby inactivated it. Since this enzyme does the first step in formation of prostaglandins, no prostaglandins are formed in aspirin-treated platelets (see Fig. 3 for a scheme of prostaglandin and leukotriene products of arachidonic acid). We next decided to do a randomized controlled trial to determine if low doses of aspirin could prevent thrombosis in man. We chose to study the occurrence of thrombi in patients with arteriovenous shunts in their arms, which are used for vascular access for hemodialysis in patients with renal failure. These shunts frequently thrombose and so a small study of short duration was adequate to achieve significant results. Common events are much easier to study as was noted above. This study was done in 1978 when clinical trials were much easier to carry out than is today. Late one afternoon, I looked in the St. Louis phone directory for aspirin and found a company in town, Rexall, that made aspirin tablets. I called after hours, and a man answered the phone. I explained what I wanted: 100 bottles of 100 tablets containing 160 mg aspirin and the same number of bottles of a matched placebo. The man said he could make them without any problem and he delivered them to my lab the next morning at no charge. We continued the study for 6 months by which time 18 of 25 patients in the placebo group had a thrombosis compared to 6 of 19 of those given aspirin for a relative reduction of 3-fold, a highly significant result (Harter et al., 1979). This experiment was later repeated several times by other groups confirming our results.

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Since these results were reported, myriad studies have been conducted to evaluate the use of aspirin in preventing heart attacks, strokes, and other thromboses. One of the early trials completed in 1989 was a primary prevention study in which healthy physicians were randomized to receive either 320 mg of aspirin or a placebo on alternate days (1989). The results were striking: fatal myocardial infarctions occurred in 10 aspirin treated patients compared to 26 in the control group. The total of infarctions was 129 in the aspirin group and 213 in the controls. Recall that when events are rare much larger sample sizes are required to obtain significant results. Since heart attacks are relatively rare in healthy physicians, a large number of subjects was required. In this study there were 342 heart attacks in over 20,000 physicians (less then 2%) These results were highly significant and led to FDA approval of aspirin for heart attack prevention. I might add that by the time this study was initiated I was already convinced that aspirin prevented heart attacks and I was taking aspirin daily. I was unwilling to be randomized into a trial where I might end up with the placebo. I refused to participate. Since this time a large number of studies of aspirin use for the prevention of thromboses in patients at high risk have been carried out. A summary of the results of 5 large studies follows. In each case the occurrence of repeated events or death are reported as percentages (Patrono et al., 2005): 1) patients with previous myocardial infarction, aspirin treated 13.5% vs 16.8% controls. 2) patients with current myocardial infarction, aspirin 10.6% vs 14.5% controls. 3) patients with previous stroke or transient stroke, symptoms aspirin 19.1% vs 21.8% controls. 4) Patients with acute stroke, aspirin 8.2% vs 9.2% controls. 5) Other high risk patients, aspirin 11.1% vs 13.4% controls. All of these results are highly significant. I conclude that aspirin reduces but does not eliminate thrombosis from all causes. Other conditions in which aspirin has shown benefit in reducing thrombosis include chronic angina pectoris, polycythemia vera, carotid artery stenosis, and atrial fibrillation. The story does not end there The Cyclooxygenase that is acetylated in platelets is the first enzyme in the pathway for formation of prostaglandins. It oxygenates arachidonic acid to form a cyclic endoperoxide. This intermediate is acted upon by several other enzymes to produce different prostaglandins including thromboxane A 2 which is the substance in platelets that activates them to aggregate. Thromboxane A 2 is also a potent vasoconstrictor. Another enzyme, prostacyclin synthetase, forms prostacyclin which is a potent vasodilator. This compound is mainly formed in endothelial cells. Prostacyclin and thromboxane A 2 antagonize each other one tending to promote thromboses and the other to prevent it. There are 2 distinct forms of cyclooxygenase both forming the same product. Cyclooxygenase 1 (Cox 1) is the main form in platelets. This enzyme is stable and active in cells in which it is expressed. Cyclooxygenase 2 (Cox2) is an inducible enzyme that is not expressed in cells until something stimulates its expression such as cytokines or growth factors. When subjects are treated with aspirin, Cox 1 in platelets and other tissues is inactivated. If Cox 2 is not induced during the treatment it is not inhibited. Its subsequent induction will lead to prostaglandin synthesis in the tissues in which it is expressed even though aspirin had been administered. Most non-steroidal anti-inflammatory drugs are not selective and inhibit both forms of cyclooxygenase. In recent years selective inhibitors specific for Cox 2 have been developed. These include Celebrex and Vioxx. Vioxx has been shown to increase the risk of cardiovascular events and has been removed from the market. A recent study indicates that suppression of Cox2 without concurrent suppression of Cox1 increases cardiovascular risk (Cannon and Cannon, 2012). These authors showed that in mice with specific deletion of vascular Cox2 there was reduced production of the vasodilator nitric oxide thereby reducing vascular relaxation. This was accompanied by an increase in hypertension and thrombosis. They showed that this effect of reducing Cox2 without blocking Cox1 fully applies to all NSAIDS except naproxine. They postulate that naproxine spares this ill effect because it has a very long half life and results in sustained inhibition of Cox1. An important role for Cox 2 in colon tumorigenesis has been shown. Mice with a deletion of the adenomatous polyposis gene develop large numbers of colon polyps starting by 10 weeks of age (Oshima et al., 1996). When these animals were bred to mice with a knockout of Cox2, the number of polyps was reduced by 90% showing that Cox 2 expression is critical for polyp development. The size of the polyps in these mice was also markedly reduced to about 1/5th the size of polyps in control mice. In this study treatment of APC gene deleted mice with a tricyclic inhibiter specific for Cox2 also resulted in markedly reduced numbers of polyps.

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Several case reports dating from the 1980s reported a decrease in polyp number in a handful of patients treated with the NSIAD drug Sulindac. The rationale for treating patients with Sulindac in these case studies is not entirely clear although the authors site several studies in rodents where NSAIDSs were found to decrease polyp development. An RCT in 22 humans with familial polyposis showed that the nonspecific Cox inhibitor Sulindac significantly reduced the number of polyps to about 1/3 of that in placebo treated patients (Giardiello et al., 1993). Results from patients treated in these studies infer that Cox 2 inhibition might alter the occurrence of colon cancer in humans. That such is the case is indicated by an observational study in man (Giovannucci et al., 1994). In this study 48,000 health professionals answered a questionnaire with a number of queries including aspirin use and the occurrence of colorectal cancer and advanced cancer (either death or metastatic disease). The questionnaires were administered in 1986, 1988, 1990, and 1992. Compliance was 95%. About 1/4 of subjects reported aspirin use (2 or more times/week) There were 251cases of colon cancer during the study. In 1986 aspirin users had only 68% as many cancers as controls. The occurrence of advanced cancer was 51% of that in controls. Remarkably, the benefit of aspirin use steadily increased with each subsequent questionnaire so that by 1992 after an average aspirin use of 9 years the incidence of colon cancer was 42 out of 30,600 nonusers and only 8 of 12,300 aspirin users. The occurrence of advanced cancer was even more strikingly reduced with 20 cancers out of 30,000 nonusers and a single advanced cancer out of 11,300 aspirin users. Aspirin use appears to have a huge benefit. Recently the large randomized trials of aspirin use to prevent cardiovascular disease were reinvestigated for the incidence of advanced colon cancer. Of over 17,000 trial participants the incidence of advanced colon cancer was reduced to 64% in aspirin users with a total of 987 cancers. These studies were all carried out with the low doses of aspirin that are needed to block platelet function. (75 mg–320 mg/day). That a significant benefit was shown indicates that large doses of aspirin are not needed to show benefit. Although it is possible that larger doses might have shown a greater benefit. It is a standard of care that all newly diagnosed patients with colon cancer should be treated with aspirin in an effort to reduce metastases. The dose to be used is uncertain although I would favor 640 mg/day as this larger dosage still has relatively low toxicity and might confer increased efficacy. Aspirin use in other forms of cancer An obvious question now arises. What is the effect of aspirin use on the incidence and spread by metastasis of other forms of cancer. The data to answer these questions are sparse but there are hints. The problem in this case is that good data are not available. For instance in most of the studies it is not possible to discern the exact amount of aspirin taken by each subject. A recent study summarizes results from almost 200 case control and cohort studies compared to the few randomized trials available (Algra and Rothwell, 2012). The results from all three types of study confirm the large benefit of aspirin in colon cancer. The benefit of aspirin is most notable in studies in which aspirin use has been continued for at least 5 years. The data on other tumors is less clear cut. There appears to be significant benefit in esophageal cancer with aspirin users having only 58% as many tumors as controls in RCT. The results from case control and cohort studies showed similar benefits. A significant benefit was also seen in gastric and breast cancer. The benefit in other cancer types was always in the direction of benefit from aspirin use but the results were not statistically significant in individual tumor types. The risk of metastasis was reduced in aspirin users in all cancer types when they were pooled together. Details of studies with various cancers will follow. Another report pooling results from the RCTs of daily aspirin use for cardioprotection shows a decrease in the 20 year death rates for all cancers (Rothwell et al., 2011). Aspirin use decreased the 20 year death rate in all GI tract cancers to 65% of that in non users. The death rate in all other solid tumors pooled was also reduced in aspirin users to 75% of that of controls. When solid tumors were considered by cell type, in most cases the results in aspirin users did not show significant benefit except for lung cancer, where the death rate was reduced to 71% in aspirin users. The authors speculate that the benefit of aspirin may have been underestimated since 40% of patients in the aspirin group had discontinued its use by 20 years.

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Breast cancer Recent results of a large cohort study of postmenopausal breast cancer were reported (Bardia et al., 2011). A questionnaire was mailed to a large number of women, aged 59 to 75, in 1992 and 25,580 responded. There were 1581 breast cancers identified and the risk was reduced by 20% in aspirin users. The benefit correlated with the frequency of aspirin use. Those who took it 6 or more days/week had a 30% reduction in breast cancer incidence. The effect was the same in hormone positive and negative tumors, suggesting that the benefit of aspirin was independent of hormone receptor status. However, a survey as part of the nurses health study reported no benefit from aspirin use. However, another report from the nurses health study data showed that aspirin use after the diagnosis of breast cancer reduced the death rate (Holmes et al., 2010). This study enrolled 4164 nurses with stages I, II, or III breast cancer between 1976 and 2002. They were observed until death or June 2006 whichever came first. Aspirin use was recorded as 0,1,2 to 5, or 6–7 days per week. There were 341 cancer deaths and aspirin use was associated with a decreased death rate. Risk rate for 1 day use was 1.07, 2–5 days risk was 0.29, 6 or 7 days risk was 0.36. For women living at least one year after breast cancer diagnosis, aspirin use was associated with a decreased rate of recurrence and death. Prostate cancer A number of case control and cohort studies have investigated the link between aspirin use and prostate cancer. Meta-analysis of these studies shows no clear link between aspirin use and prostate cancer. The subject is very difficult to study because of the peculiar nature of this tumor. Autopsy studies of men over the age of 70 show that over 50% of men have prostate cancer and yet the death rate from this tumor is only about 3% of men. Therefore the majority of patients with this cancer do not die from it. It is possible that aspirin use decreases the actual incidence of prostate cancer but the effect is not detectable from the clinical data on the small number of men who actually manifest the disease. Recently a large study of patients with prostate cancer was reported. 5955 men were treated with either radical prostatectomy or radiation therapy and were subsequently followed for 10 years (24). Because these patients are mostly elderly they had many comorbid conditions that resulted in many patients receiving anticoagulant therapy. There were 2175 patients receiving anticoagulants, mostly aspirin (84%). After a median follow-up of 70 months prostate cancer specific mortality was markedly reduced in the anticoagulant group. The death rate at 10 years was reduced from 8% to 3% (p < 0.01). Thus in patients with clinically significant prostate cancer aspirin provides a large survival advantage. Lung cancer and skin cancer The meta-analysis mentioned above (Bardia et al., 2011) reported a decreased death rate after aspirin in lung cancer with most of the benefit from adenocarcinomas. A more recent meta-analysis (Xu et al., 2012) only showed benefit from aspirin in patients taking 7 or more tablets/week. The benefit was about 20%. In a study of aspirin use as adjuvant therapy after resection of non small cell lung cancer, aspirin use was associated with a 5% increased survival which although small was statistically significant. Overall, the data on lung cancer show slight benefit. Data on skin cancer has appeared in a very recent population-based case control study in northern Denmark (Johannesdottir et al., 2012). In this study all skin cancers including squamous cell, Basal cell, and malignant melanoma were identified from records for the period 1991 to 2008. There were 1921 Squamous Cell Cancers, 12,864 Basal Cell Cancers, and 3089 Melanomas. 10 age, sex, and, county of origin matched controls were selected for each case. Use of aspirin and other NSAIDS was determined by prescription records which indicated a measure of both magnitude and duration of use. Aspirin and NSAID use was associated with decreased cancer risk with the largest effects seen with prolonged (>7 years) and higher use. The risk of Squamous cell cancer was reduced to 65% among long term high intensity users. Basal cell cancers were reduced to 83% and Malignant Melanoma was reduced to 54%. It appears that aspirin and other NSAID use has a large benefit when use is prolonged and steady. It is not possible from the data presented to know the exact doses of drug used.

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Aspirin intolerance and resistance Intolerance to aspirin is infrequent and ranges from 0.3 to 2.0% in various studies (Jenneck et al., 2007). The incidence increases in subjects with asthma rising to 10% or more. The Samter triad is asthma, nasal polyps, and aspirin intolerance, which occurs in up to 20% of patients with asthma and nasal polyps. Aspirin intolerance is thought to arise from an imbalance between the prostaglandin synthesis pathway that is in general anti-inflammatory and the leukotriene synthesis pathway that is pro-inflammatory. Leukotrienes are also oxygenated products of arachidonic acid. When Cox enzymes are inhibited by aspirin more arachidonic acid is diverted to leukotriene production resulting in asthma. There are protocols for “desensitizing “ patients to aspirin but they have not been widely applied. Aspirin resistance is a phenomenon ascribed to the results of various in vitro tests of platelet function which suggest that the usual low doses of aspirin may not be adequate in some patients. However in vitro platelet function tests show little correlation with in vivo findings. Furthermore since only about 1/3 of thrombotic events are prevented by aspirin it is clear that other factors are important in the pathogenesis of thrombosis. It seems wrong to alter antiplatelet therapy based on the fact that a thrombosis occurred while taking aspirin. Perhaps the “next” thrombosis would be prevented by aspirin. Aspirin toxicity Aspirin toxicity is dose related as mentioned previously. A Dutch study of patients taking low dose aspirin for thrombosis prevention found that in a series of 947 patients 6.6% discontinued therapy at some point (Tournoij et al., 2009). However only half of these patients discontinued aspirin because of side effects. The rest had other reasons including just noncompliance with medication or disinterest in the therapy. A more rigorous meta-analysis has recently appeared (Lanas et al., 2011). These authors reviewed all of the low dose aspirin RCT studies. The risk of major GI bleed was 1.55. This equates to 1 bleed for every 500 patients treated. There were no fatal bleeds among the 87,600 patients studied. About 1 in 70 patients had some mild bleeding. The overall toxicity of aspirin therapy is quite low. In my own case I have taken 640 mg of aspirin daily for 35 years without any known toxicity. Other toxic effects of aspirin are much rarer including rash, thrombocytopenia, and dyspepsia and were not increased the RCTs. Another group of patients in whom aspirin is especially toxic has been described by A. J. Quick (1970). Patients with hemophilia A may have severe bleeding after aspirin ingestion. Quick devised an aspirin tolerance test to assess the risk. He measured the skin bleeding time before and after a dose of aspirin (usually 650 mg) He described several patients with hemophilia in which the bleeding time went from 3 to 4 min before aspirin to 20–30 min after aspirin. In some cases bleeding recurred after initial cessation and persisted for several days. He concluded that aspirin was contraindicated in hemophiliacs. This creates a difficult situation since the most prominent symptom in hemophilia is pain. Several of his patients continued taking aspirin even knowing the dangers because of the pain relief obtained with aspirin. Who should take aspirin and how much? I believe that all adults should take an aspirin daily unless they are among the few per cent of the population that cannot tolerate the drug. Some would argue that the benefits in a relatively young and healthy population are very small as the incidence of cancers and heart disease is small. Although the physicians health study was done in a largely healthy population and there was a clear benefit (Roth and Majerus, 1975). Reduction in advanced colon cancer, which is the second leading cause of cancer death in the USA, approaches 50%. Because events are rare in healthy populations any RCT of prophylactic aspirin use would require an enormous study of prolonged duration. However just because it is hard to prove benefit does not mean that it doesn’t exist. This measure is cheap with minimal toxicity. The dose to be taken is not clear. The cardiovascular benefit of aspirin is fully achieved by 50–75 mg/day. Children’s aspirin is 81 mg/tablet while the common size for adult aspirin is 325 mg. Generic versions of these sizes are about the same price at $10./1000 tablets. There is no evidence that branded aspirin which is much more expensive is in any way superior to the generic versions. The

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simplest regimen is 325 mg/day. It seems important that the use is daily as this fact proved important in several RCT’s. I take 2 tablets/day for two reasons: 1) 640 mg of aspirin has a sedative effect and aids in sleep if taken at bedtime. 2). While RCT’s in colon cancer show benefit at low cardioprotective aspirin doses, it is possible, although not proven, that higher doses might produce larger beneficial effects. Prolonged use seems important as in several trials for cancer prevention the results improved over a 5– 10 year period of taking aspirin. So have at it people – TAKE YOUR ASPIRIN! References Algra AM, Rothwell PM. Effects of regular aspirin on long-term cancer incidence and metastasis: a systematic comparison of evidence from observational studies versus randomised trials. Lancet Oncol 2012;13:518–27. Bardia A, Olson JE, Vachon CM, Lazovich D, Vierkant RA, Wang AH, et al. Effect of aspirin and other NSAIDs on postmenopausal breast cancer incidence by hormone receptor status: results from a prospective cohort study. Breast Cancer Res Treat 2011; 126:149–55. Cannon CP, Cannon PJ. Physiology. COX-2 inhibitors and cardiovascular risk. Science (New York, NY) 2012;336:1386–7. Final report on the aspirin component of the ongoing physicians’ health study. Steering committee of the physicians’ health study research group. N Engl J Med 1989;321:129–35. Fisher RB. Joseph Lister 1827–1912: The great surgeon who pioneered antiseptics and revolutionized 19th century medicine. Stein and Day; 1977. Giardiello FM, Hamilton SR, Krush AJ, Piantadosi S, Hylind LM, Celano P, et al. Treatment of colonic and rectal adenomas with sulindac in familial adenomatous polyposis. N Engl J Med 1993;328:1313–6. Giovannucci E, Rimm EB, Stampfer MJ, Colditz GA, Ascherio A, Willett WC. Aspirin use and the risk for colorectal cancer and adenoma in male health professionals. Ann Intern Med 1994;121:241–6. Harter HR, Burch JW, Majerus PW, Stanford N, Delmez JA, Anderson CB, et al. Prevention of thrombosis in patients on hemodialysis by low-dose aspirin. N Engl J Med 1979;301:577–9. Holmes MD, Chen WY, Li L, Hertzmark E, Spiegelman D, Hankinson SE. Aspirin intake and survival after breast cancer. J Clin Oncol 2010;28:1467–72. Jenneck C, Juergens U, Buecheler M, Novak N. Pathogenesis, diagnosis, and treatment of aspirin intolerance. Ann Allergy Asthma Immunol 2007;99:13–21. Johannesdottir SA, Chang ET, Mehnert F, Schmidt M, Olesen AB, Sorensen HT. Nonsteroidal anti-inflammatory drugs and the risk of skin cancer: a population-based case-control study. Cancer 2012;118:4768–76. Lanas A, Wu P, Medin J, Mills EJ. Low doses of acetylsalicylic acid increase risk of gastrointestinal bleeding in a meta-analysis. Clin Gastroenterol Hepatol 2011;9:762–8. e6. Mann CC, Plummer ML. The aspirin wars: money, medicine, and 100 years of rampant competition. Knopf; 1991. Oshima M, Dinchuk JE, Kargman SL, Oshima H, Hancock B, Kwong E, et al. Suppression of intestinal polyposis in Apc delta716 knockout mice by inhibition of cyclooxygenase 2 (COX-2). Cell 1996;87:803–9. Patrono C, Garcia Rodriguez LA, Landolfi R, Baigent C. Low-dose aspirin for the prevention of atherothrombosis. New Engl J Med 2005;353:2373–83. Quick AJ. Hemophilia and new hemorhagic states. UNC press; 1970. Rainsford KD. Aspirin and the salicylates. Butterworths; 1984. Roth GJ, Majerus PW. The mechanism of the effect of aspirin on human platelets. I. Acetylation of a particulate fraction protein. J Clin Invest 1975;56:624–32. Rothwell PM, Fowkes FG, Belch JF, Ogawa H, Warlow CP, Meade TW. Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomised trials. Lancet 2011;377:31–41. Smith JB, Willis AL. Aspirin selectively inhibits prostaglandin production in human platelets. Nat New Biol 1971;231:235–7. Tournoij E, Peters RJ, Langenberg M, Kanhai KJ, Moll FL. The prevalence of intolerance for low-dose acetylsalicylacid in the secondary prevention of atherothrombosis. Eur J Vasc Endovasc Surg 2009;37:597–603. Vane JR. Inhibition of prostaglandin synthesis as a mechanism of action for aspirin-like drugs. Nat New Bio 1971;231:232–5. Weiss HJ, Aledort LM, Kochwa S. The effect of salicylates on the hemostatic properties of platelets in man. The Journal of clinical investigation 1968;47:2169–80. Xu J, Yin Z, Gao W, Liu L, Wang R, Huang P, et al. Meta-analysis on the association between nonsteroidal anti-inflammatory drug use and lung cancer risk. Clin Lung Cancer 2012;13:44–51.