Concomitant Abdominal Aortic Aneurysm and Colorectal Cancer: A Decision Analysis Approach to a Therapeutic Dilemma Vic Velanovich, MD, Charles A. Andersen, MD, Tacoma, Washington
The therapeutic approach to a patient with concomitant abdominal aortic aneurysm and colorectal carcinoma is not clear. Decision analysis helps clarify decision options and quantify therapeutic outcomes. Variables used in decision analysis include life expectancy after resection for colorectal cancer and abdominal aortic aneurysm, rupture rate of abdominal aortic aneurysm, complications of colorectal cancer, complications of abdominal aortic aneurysmorrhaphy, and colorectal resection. The results support the concept that the symptomatic lesion should be treated first. When both lesions are asymptomatic and the aneurysm is 4 - 5 cm in diameter, it should be resected first, if the colorectal cancer has a < 5 % chance of obstruction or perforation, as is found in noncircumferential lesions. When the aneurysm is > 5 cm, it should be resected first if the cancer has a < 2 2 % chance of obstructing or perforating, as with circumferential lesions. Simultaneous resection should be considered for patients with aneurysms > 5 cm and cancers with a > 7 5 - 8 0 % chance of obstruction or perforation, provided the dual procedures can be performed with a < 1 0 % operative mortality and < 5 0 % complication, rate. Ann Vasc Surg 1991;5:449455). KEY WORDS:
Abdominal aortic aneurysm; colorectal cancer; decision analysis.
Szilagyi and colleagues [1] were the first to report the concomitant o c c u r r e n c e of an abdominal aortic aneurysm (AAA) and a malignancy. They found that the incidence of malignancies in patients with AAA was 4%. Since then, others have reported incidences of 2 to 4% [2,3]. The incidence of colon carcinoma in patients with AAA has been reported to be 0.5 to 3.8% [2,4-6].
From the General and Vascular Surgery Services, Department of Surgery, Madigan Army Medical Center, Tacoma, Washington. Reprint requests: CPT Vic Velanovich, MC General Surgery Service, Department of Surgery, Madigan Army Medical Center, Tacoma, Washington 98431. The views expressed in this article are those of the author and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the United States Government.
The therapeutic approach to a patient with coexisting AAA and colorectal carcinoma is not always clear. Lobbato and associates [4] reported a survey of 46 professors of general and vascular surgery with no consensus as to which problem should be given treatment priority. Few studies have attempted to determine treatment priority. Nora and coworkers [6] have recommended that, if the carcinoma is asymptomatic, then the aneurysm should be resected first. H o w e v e r , guidelines as to when an asymptomatic colon cancer should be resected first are not given. Decision analysis is a method whereby all relevant data about a particular problem may be quantitatively assessed to determine the best treatment option [7,8]. In this study, we use decision analysis to determine the therapeutic approach to the dilemma of concomitant AAA and colorectal cancer. 449
450
ANNALS OF VASCULAR SURGERY
C O N C O M I T A N T A A A A N D COLORECTAL CANCER
Nothing For Either
II
Resect AAA 1st, Nothing For Ca
II
Resect Ca 1st, Nothing For AAA 0
Figure 2
0
Figure 3
0
Figure 4
O
Figure 5
Patient With AAA And Colorectal Ca
Resect Ca 1st, Then AAA
Resect AAA l st, Then Ca
Resect Both At Same Time
Fig. 1. Choices for management of patients with concomitant abdominal aortic aneurysms and colorectal cancers. See figure associated with stated treatment choice for probable outcome.
METHODS AND MATERIALS Decision analysis is done by quantifying the possible outcomes of the choices available to the physician. A detailed description of the technique can be found in Weinstein and Fineberg [7]. Briefly, a decision tree is constructed with choice nodes and chance nodes. A choice node (visually represented as a square (El]) is a point in the decision process at which the physician chooses among the options available. The chance node (visually represented by a circle, o) is a point from which possible outcomes stem. Each outcome branch has a certain probability of occurring; this probability is derived from the literature or expert opinion. The unit of measurement in a decision analysis is the quality-adjusted life expectancy (QALE). This is measured in years. It is derived by determining the life expectancy (LE) of a given therapeutic maneuver for a particular disease process. The quality multiplier (QM) is the quality of life level for the patient after the treatment is concluded. For example, the QM for someone after an appendectomy for acute appendicitis is 1.0--that is, the patient returns to the quality of life level enjoyed prior to his illness. A QM for someone requiring a hemipelvectomy for proximal lower extremity sarcoma may be 0.5--that is, his quality of life is half of what it was prior to the surgery. Therefore, if a patient's LE after a particular treatment option is 10 years and his QM is 0.8, then his QALE is eight years. Another adjustment on the QALE is the shortterm morbidity (STM). This is affected by things such as postoperative complications which prolong
hospital stay or otherwise adversely affect treatment outcome but are completely reversible--as opposed to irreversible outcomes which permanently lower QMs. The STM is merely subtracted from the LE to determine its effect on the QALE. Because the effects of the various components used to determine the QALE vary, sensitivity analysis is used to determine these effects. In sensitivity analysis a particular component of the decision tree, e.g., complication rate, is varied while other components are held constant. In this way, we can determine the effects of a high complication rate versus a low complication rate on the QALE. The LEs, QMs and STMs used in this decision analysis were determined from the literature on the treatment of AAA, colorectal carcinoma, and coexistent diseases [1-5, 9-27].
RESULTS Figure I depicts the choices available to the surgeon treating a patient with coexisting colorectal cancer and an AAA. An aortic aneurysm will be defined as one with aortic dilation greater than 4 cm. The first option, to do nothing for either disease, would only be considered for those patients with other end-stage illnesses or so severely diseased that they would be expected to die within a few weeks. This option will not be addressed in this study. The second option, resection of the AAA with no surgical therapy for the carcinoma, would only be considered in patients with very large symptomatic aneurysms and widely disseminated
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No 5 - 1991
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CONCOMITANT AAA AND COLORECTAL CANCER
metastatic cancer. This option also will not be subject to decision analysis. There are six issues involved when deciding the course of action in a patient with AAA and colon carcinoma: (I) L E after resection of the AAA: (2) LE after resection of the carcinoma; (3) chance of rupture of the AAA after resection of the carcinoma but prior to repair of the AAA; (4) chance of graft infection of an AAA repair after carcinoma resection; (5) chance of a carcinoma-related complication (i.e., obstruction or perforation) after a AAA repair but prior to carcinoma resection; and (6) operative mortality. After AAA repair LE essentially becomes age, sex, race and disease-specific for persons without AAA [9,26]. Therefore, the limiting LE for these patients is related to the carcinoma. Figures 2 to 5 represent the decision outcomes of the treatment options presented. Figure 2 shows the possible clinical outcomes of a patient who undergoes a resection of his colon cancer with nothing done about his AAA. The Q A L E of this decision is 5.82 years. Although the Dukes classification is the standard prognostic index, the Dukes classification of any particular patient prior to resection is unknown; therefore, the L E used in this decision analysis is estimated from the overall five-year survival reported in the literature [ 13,15,17]. Estimates of the probability of AAA rupture after resection of the carcinoma are estimated from reported rates [1,2,5,12,14] based on an eight week recovery period between operations. No data exist pertaining to the rate of known colorectal cancer obstruction or perforation. Indeed the accumulation of such data would be unethical since the standard of practice requires that colorectal cancers be resected in an expedient manner. It can be assumed that small colorectal cancer lesions would be at low risk and large or circumferential lesions would be at high risk. The rate of 10% used in Figure 2 is an estimate; therefore, particular attention to the sensitivity analysis of this component of the decision analysis is extremely important. Similarly, the rate of graft infection in patients who have recently undergone colorectal surgery is unknown--primarily because the fear of graft infection from bowel contaminants is so high that surgeons in general wait several weeks to months after colorectal surgery to proceed with AAA surgery [5]. The percentages used in Figures 3 and 4 are also estimates, so there is increased importance on the sensitivity analysis. Short-term morbidity is based on the rates and types of complications seen in these procedures [3,6,11,13,15, 17,19-21,23,26]. Appropriate estimates based on the literature were used for obstructing or perforating carcinomas [ 15,16,18,25,27]. Figure 3 shows the possible outcomes of a patient who undergoes a resection of his colon carcinoma, followed by repair of his AAA eight weeks later. The Q A L E is 6.13 years. His Q A L E depends on the aneurysm rupture rate for this eight week period
Uncompl Surgery icated < 71%
/ Complicated < (~ ~ Surgery 5%,STM=0.03yrs
NoAAARupture II 66.2% AAARupture < 33.8% NoAAARupturc II 66.2% AAARupture < 33.8%
Death FromSurgery 11 4%
Repair 50% Death II 50% Repair II 50% Death II 50%
Fig. 2. Outcome if cancer is resected and nothing done for aneurysm. Quality multiplier for those who survive is 0.97, for death is 0. Seventy-one percent of patients will have uncomplicated surgery; 25% will have complicated surgery with short-term morbidity of 10 days; 4% will die from the procedure; 66.2% will not rupture their aneurysms, while 33.8% will. Of those that rupture, 50% will die. Overall quality-adjusted life expectancy is 5.82 years.
and the risk of graft infection after large bowel surgery. For AAA of 4-5 cm, the estimated probability of rupture is 2.4% over eight weeks; for those 5 cm, it is 10.7% [1,2,5,22,24]. We may assume the consequences of a graft infection are a 10% mortality either secondary to sepsis or reoperation. See Table I for the results of the sensitivity analysis. Figure 4 represents the possible outcomes of repairing the AAA first, followed by resection of the cancer eight weeks later. The Q A L E is 6.02 years. This depends on the rate of perforation or obstruction for the carcinoma, which substantially increases the morbidity and mortality of a colonic resection [16,18,25,27]. The Q A L E is higher for the choice of AAA resection first when the aneurysm is TABLE I.--Sensitivity analysis Operation Resection of Ca first, followed by AAA repair (Fig. 4) Repair AAA first, followed by Ca resection (Fig. 2) Combined resection AAA and Ca (Fig. 5) QALE = Quality-adjusted a b d o m i n a l aortic a n e u r y s m
Parameters AAA < 5 cm AAA > 5 cm Graft infection 0% Graft infection 100% Ca complication 0% Ca complication 100% Operative mortality 5% Operative mortality 35% Graft infection 0% Graft infection 100%
life e x p e c t a n c y ;
Ca -
Colon carcinoma;
QALE 6.21 5.61 6.15 5.27 6.37 2.85 6.76 4.48 6.44 5.72 AAA
=
452
ANNALSOF VASCULARSURGERY
C O N C O M I T A N T AAA A N D COLORECTAL CANCER
Uncomplicated AAA Resection
Uneventful ~ Recovery 94.8%
[]
65% ComplicatedAAAResection 30%, Sa'M 008 yr II Death 5%
II
Uncomplicated Resection
71% SurgicalRepair 50%
II
Death 50%
II
Aortic Rupture 5.2%
Uncomplicated AAA Resection
]]
65% I
Uneventful Recovery 94.8%
Complicated AAA Resection
[[
30%,STM0.08yr Death 5%
II
Complicated Resection
25%,STM0.03yr SurgicalRepair 50%
[I
Death 50%
II
Rupture 5.2%
Death
.[I
4% Fig. 3. Outcome for resection of cancer first, followed by repair of aneurysm eight weeks later. Quality multiplier for survival is 0.96, for death O. Patients with an uneventful recovery after colon surgery number 94.8%; 5.2% will have aneurysmal rupture. Of those with uneventful recovery, 65% will have uncomplicated abdominal aortic aneurysm repairs, 30% complicated repair, and 5% will die perioperativety. Overall qualityadjusted life expectancy is 6.13 years.
4-5 cm and the carcinoma has a 5 cm, the QALE is higher for AAA resection first if the carcinoma has less than a 22% chance of obstructing or perforating (see Table I).
Figure 5 shows the outcomes of repairing the AAA and resecting the carcinoma during the same operation. The QALE is 6.20 years. This is dependent on the operative mortality of this combined procedure and the graft infection rate (see Table I).
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CONCOMITANT AAA A N D COLORECTAL CANCER
453
Uncomplicated Ca Resection I I 71% Uneventful Recovery
Complicated Ca Resection
90%
25%, STM 0.03 yr
Death
I[
4%
II
Emergency Resection Uncomplicated
[[
Uncomplicated Resection 80%
57% Complication
Emergency Resection Complicated
10%
30%, STM 0.06 yr
II
Death
13%
II
Uncomplicated Ca Resection ] ] 71%
Recovery
Complicated Ca Resection
90%
25%, S T . 0.o3 yr
II
Death 4~
II
Emergency Resection Uncomplicated
1]
Complicated Resection 15%. STM 0.03 yr
57%
Death
Ca Complication
Emergency Resection Complicated
10%
30%, STM 0.06 yr
II II
Death
II
13%
5%
Fig. 4. Outcome for resection of aneurysm first, followed by resection of cancer. Quality multiplier for survival is 0.97, and for death 0. Eighty percent of patients will have uncomplicated abdominal aortic aneurysm (AAA) repairs; 15% will have complicated repairs; 5% will die perioperatively. Of patients who survive AAA repair, 90% will recover without carcinoma-related complications, and 10% will have carcinoma-related complications. Of these patients with cancer-related complications, 57% will have uncomplicated emergency resections, 30% complicated emergency resections, and 13% perioperative death. Overall quality-adjusted life expectancy is 6.02 years.
454
C O N C O M I T A N T AAA A N D COLORECTAL CANCER
DISCUSSION Decision analysis helps quantitate the most probable outcomes of therapeutic choices. It is especially helpful in those clinical problems for which a definitive, controlled clinical trial has not been done. Decision analysis considers all possible outcomes, makes explicit all the assumptions about a clinical problem, and considers the quality of these outcomes [8]. Although decision analysis has been resisted by some physicians because it supposedly takes the art out of medicine, it is very similar to the algorithms of clinical choices published on a variety of disease diagnoses and therapies, except that the familiar concept of life expectancy, therapeutic morbidity and mortality, and quality of life are explicit and quantified. These advantages make decision analysis an excellent tool for determining the best treatment options for patients with concomitant A A A and colorectal cancer. The essential features that determine the priority of treatment in a patient with coexisting A A A and colorectal carcinoma are the aneurysmal rupture rate, rate of graft infection, and rate of cancerassociated complications. The rupture rate of aneurysms is related to their size [19,21]. In addition, laparotomy itself may increase the chance of rupture [14]. Reported rates of this complication vary between 0 and 30% [1,3,4,8,10]. The average of these reported rates standardized for an eight week period was used in this study. By sensitivity analysis, the QALE with a rupture rate of 0 would be 6.28 years and with a rupture rate of 23%, 5.60 years. Since the chance of rupture also depends on the size of the aneurysm, sensitivity analysis showed that AAAs 4-5 cm in diameter had a 2.4% chance of rupture while those >5 cm had a 10.7% chance. This had a significant effect on the QALE of patients who were operated upon for colon carcinoma first. Therefore, the size of the AAA as well as prior laporotomy had significant influence on the rate of AAA rupture. Graft infection after AAA repair is a devastating UncomplicatedResection
II
60% Complicated Resection
I[
30%, STM 0.08 yr Death
10%
II
Fig. 5. Outcome for resection of both aneurysm and cancer, simultaneously. Quality multiplier for survival is 0.96, for death 0. Overall quality-adjusted life expectancy is 6.20 years.
ANNALS OF VASCULAR SURGERY
complication. Although some feel that combining AAA repair with other gastrointestinal procedures is a safe and acceptable practice [10], others recommend that gastrointestinal operations should be avoided during aortic surgery [5]. There are no reported data on the incidence of aortic graft infection, either with concomitant colorectal surgery or shortly following or preceding colorectal surgery. For the decision tree depicted in Figure 3 (resection of colon carcinoma first, followed by repair of AAA), a 0% infection rate would yield a QALE of 6.15 years and a 100% rate, 5.77 years. There is a similar drop in the QALE from 6.44 years to 5.72 years when concomitant resections are performed. Individual surgeons and institutions may have their own experience or judgment as to what the graft infection rate would be and would be able to use their figures to determine the most appropriate treatment options using the data presented here. Although the rate of cancer-related complications is important in determining the QALE, how to determine this probability in the clinical setting is problematic. Most asymptomatic colorectal cancers can be inspected by proctoscopy or colonoscopy. This may help the surgeon determine if the lesion is at low risk for obstruction or perforation (i.e., 5% chance) or at high risk (i.e., >25% chance). For example, small lesions may be considered at low risk, while large, circumferential lesions may be considered at high risk. Raftery and Samson [15] have correlated the presenting symptoms of colorectal cancer with survival. Perforation and obstruction were poor prognostic signs, in addition to pain, weight loss and abdominal mass. This information may also be of benefit to the surgeon in determining the patient's chances of developing carcinoma-related complications. Colorectal carcinomas that lead to obstruction or perforation are very aggressive tumors and carry much worse prognoses than those that do not cause complications, and these complicated tumors are associated with higher operative morbidity and mortality [16,18,25,27]. However, recognition of those cancers at risk for impending complications will sway the surgeon to resection of the carcinoma prior to the AAA. Decision analysis, like clinical judgment, is only as good as the information available. Not enough information is available on the natural history or therapeutic results for patients who have coexisting AAA and colorectal carcinoma. Estimates from the literature can be made for AAA rupture. However, aortic graft infection rates and carcinoma obstruction and perforation rates are almost entirely unknown. When reviewing the decision trees and sensitivity analyses of this decision analysis, the reader is encouraged to recall his or her own experience with graft infections and carcinomarelated complications. Although these uncertainties
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CONCOMITANT AAA A N D COLORECTAL CANCER
p o s e limitations to the decision analysis presented, this is no different than the limitations imposed on nonquantitative clinical judgment and serves to e m p h a s i z e those areas of ignorance we have with regard to the clinical problem of coexisting A A A and colorectal cancer.
CONCLUSIONS In conclusion, concomitant A A A and colorectal carcinoma is a difficult m a n a g e m e n t problem. In general, the symptomatic lesion should be treated first. W h e n both lesions are asymptomatic, a A A A < 5 cm should be resected first if the carcinoma has a < 5 % chance of b e c o m i n g complicated. If the A A A is > 5 cm, then it should be resected first, if the carcinoma has a < 2 0 - 2 5 % chance of becoming complicated. Simultaneous reactions may be considered if the A A A is > 5 cm and the carcinoma has a > 7 5 - 8 0 % chance o f obstruction or perforation. Individual surgeons must temper these r e c o m m e n dations based on their o w n success rate and complication rate with these operations.
REFERENCES 1. SZILAGYI DE, ELLIOT JP, BERGUER R. Coincidental malignancy and abdominal aortic aneurysm: problems of management. Arch Surg 1967:95:402-41 I. 2. MORRIS DM, COLQUITT J. Concomitant abdominal aortic aneurysm and malignant disease: a difficult management problem. J Surg Oncol 1988:39:122-125. 3. FIELDING JWL, BLACK J, ASHTON F, et al. Diagnosis and management of 528 abdominal aortic aneurysms. Br M e d J 1981:283:355-359. 4. LOBBATO V J, ROTHENBERG RE, LA RAJA RD, et al. Coexistence of abdominal aortic aneurysm and carcinoma of the colon: a dilemma. J Vasc Surg 1985;2:724-726. 5. HUGH TB, MASSON J, GRAHAM AR, et al. Combined gastrointestinal and abdominal aortic aneurysm operations. Aust N Z J Surg 1988;58:805-810. 6. NORA JD, PAIROLERO PC, N1VATVONGS S, et al. Concomitant abdominal aortic aneurysm and colorectal carcinoma: priority of resection. J Vasc Surg 1989;9:630-636. 7. WEINSTEIN MC, FINEBERG HV. Clinical decision analysis. Philadelphia: WB Saunders Co., 1980. 8. PAUKER SG, KASSIRER JP. Decision analysis. N Engl J M e d 1987;316:250-258.
mmm
455
9. SZILAGYI DE, SMITH RF, DE RUSSO FJ, et al. Contribution of abdominal aortic aneurysmectomy to prolongation of life. Ann Surg 1966;164:678~97. 10. TOMPKINS WC, CHAVEZ CM, CONN JH, et al. Combining intraabdominal arterial grafting with gastrointestinal or biliary tract procedures. Am J Surg 1973;136:598~00. 11. JOHNSON WC, NABSETH DC. Visceral infarction following aortic surgery. Ann Surg 1974:180:312-318. 12. TRUEBLOOD HW, WILLIAMS DK, GUSTAFSON JR. Aneurysmal rupture following resection of abdominal malignancy. A m Surg 1976;42:535-537. 13. ,HUGHES ESR, MCDERMOTT FT, MASTERTON JP, et al. Operative mortality following excision of the rectum. Br J Surg 1980:67:49-51. 14. SWANSON RJ, LITTOOY FN, HUNT TK, et al. Laparotomy as a precipitating factor in the rupture of intra-abdominal aneurysms. Arch Surg 1980;115:299-304. 15. RAFTERY TL, SAMSON N. Carcinoma of the colon: a clinical correlation between presenting symptoms and survival. Am Surg, 1980;46:600~506. 16. KELLEY WE Jr, BROWN PW, LAWRENCE W, et al. Penetrating, obstructing and perforating carcinomas of the colon and rectum. Arch Surg 1981;116:381-384. 17. LEA JW, COVINGTON K, MC SWAIN B, et al. Surgical experience with carcinoma of the colon and rectum. Ann Surg 1982;195:600-607. 18. OHMAN U. Prognosis in patients with obstructing colorectal carcinoma. Am J Surg 1982;143:742-747. 19. DIEHL JT, CALI RF, HERTZER NR, et al. Complications of abdominal aortic reconstruction: an analysis of perioperative risk factors in 557 patients. Ann Surg 1983;197:49-56. 20. DALY JM, DE COSSE JJ. Complications in surgery of the colon and rectum. Surg Clin North A m 1983;63:1215-1231. 21. BICKERSTAFF LK, HOLLIER LH, VAN PEENEN HJ, et al. Abdominal aortic aneurysm repair combined with a second surgical procedure: morbidity and mortality. Surge~ 1984:95:487-491. 22. BERNSTEIN EF, CHAN EL. Abdominal aortic aneurysm in high risk patients: outcome of selective management based on size and expansion rate. Ann Surg 1984;200:255263. 23. CROWSON M, FIELDING JWL, BLACK J, et al. Acute gastrointestinal complications of infrarenal aortic aneurysm repair. Br J Sarg 1984;71:825-828. 24. CRONENWETT JL, MURPHY TF, ZELENOCK GB, et al. Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985;98:472483. 25. BUECHTER KJ, BOUSTANY C, CAILLOUETTE R, et al. Surgical management of the acutely obstructing colon: a review of 127 cases. A m J Surg 1988;156:163-168. 26. CHEATLE TR, SCURR JH. Abdominal aortic aneurysms: a review of current problems. Br J Surg 1989;76:826-829. 27. SERPELL JW, MCDERMOTT FT, KATRIVESSIS H, et al. Obstructing carcinomas of the colon. Br J Surg 1989:76;965-969.
The therapeutic approach to a patient with concomitant abdominal aortic aneurysm and colorectal carcinoma is not clear. Decision analysis helps clarify decision options and quantify therapeutic outcomes. Variables used in decision analysis include life expectancy after resection for colorectal cancer and abdominal aortic aneurysm, rupture rate of abdominal aortic aneurysm, complications of colorectal cancer, complications of abdominal aortic aneurysmorrhaphy, and colorectal resection. The results support the concept that the symptomatic lesion should be treated first. When both lesions are asymptomatic and the aneurysm is 4 - 5 cm in diameter, it should be resected first, if the colorectal cancer has a < 5 % chance of obstruction or perforation, as is found in noncircumferential lesions. When the aneurysm is > 5 cm, it should be resected first if the cancer has a < 2 2 % chance of obstructing or perforating, as with circumferential lesions. Simultaneous resection should be considered for patients with aneurysms > 5 cm and cancers with a > 7 5 - 8 0 % chance of obstruction or perforation, provided the dual procedures can be performed with a < 1 0 % operative mortality and < 5 0 % complication, rate. Ann Vasc Surg 1991;5:449455). KEY WORDS:
Abdominal aortic aneurysm; colorectal cancer; decision analysis.
Szilagyi and colleagues [1] were the first to report the concomitant o c c u r r e n c e of an abdominal aortic aneurysm (AAA) and a malignancy. They found that the incidence of malignancies in patients with AAA was 4%. Since then, others have reported incidences of 2 to 4% [2,3]. The incidence of colon carcinoma in patients with AAA has been reported to be 0.5 to 3.8% [2,4-6].
From the General and Vascular Surgery Services, Department of Surgery, Madigan Army Medical Center, Tacoma, Washington. Reprint requests: CPT Vic Velanovich, MC General Surgery Service, Department of Surgery, Madigan Army Medical Center, Tacoma, Washington 98431. The views expressed in this article are those of the author and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the United States Government.
The therapeutic approach to a patient with coexisting AAA and colorectal carcinoma is not always clear. Lobbato and associates [4] reported a survey of 46 professors of general and vascular surgery with no consensus as to which problem should be given treatment priority. Few studies have attempted to determine treatment priority. Nora and coworkers [6] have recommended that, if the carcinoma is asymptomatic, then the aneurysm should be resected first. H o w e v e r , guidelines as to when an asymptomatic colon cancer should be resected first are not given. Decision analysis is a method whereby all relevant data about a particular problem may be quantitatively assessed to determine the best treatment option [7,8]. In this study, we use decision analysis to determine the therapeutic approach to the dilemma of concomitant AAA and colorectal cancer. 449
450
ANNALS OF VASCULAR SURGERY
C O N C O M I T A N T A A A A N D COLORECTAL CANCER
Nothing For Either
II
Resect AAA 1st, Nothing For Ca
II
Resect Ca 1st, Nothing For AAA 0
Figure 2
0
Figure 3
0
Figure 4
O
Figure 5
Patient With AAA And Colorectal Ca
Resect Ca 1st, Then AAA
Resect AAA l st, Then Ca
Resect Both At Same Time
Fig. 1. Choices for management of patients with concomitant abdominal aortic aneurysms and colorectal cancers. See figure associated with stated treatment choice for probable outcome.
METHODS AND MATERIALS Decision analysis is done by quantifying the possible outcomes of the choices available to the physician. A detailed description of the technique can be found in Weinstein and Fineberg [7]. Briefly, a decision tree is constructed with choice nodes and chance nodes. A choice node (visually represented as a square (El]) is a point in the decision process at which the physician chooses among the options available. The chance node (visually represented by a circle, o) is a point from which possible outcomes stem. Each outcome branch has a certain probability of occurring; this probability is derived from the literature or expert opinion. The unit of measurement in a decision analysis is the quality-adjusted life expectancy (QALE). This is measured in years. It is derived by determining the life expectancy (LE) of a given therapeutic maneuver for a particular disease process. The quality multiplier (QM) is the quality of life level for the patient after the treatment is concluded. For example, the QM for someone after an appendectomy for acute appendicitis is 1.0--that is, the patient returns to the quality of life level enjoyed prior to his illness. A QM for someone requiring a hemipelvectomy for proximal lower extremity sarcoma may be 0.5--that is, his quality of life is half of what it was prior to the surgery. Therefore, if a patient's LE after a particular treatment option is 10 years and his QM is 0.8, then his QALE is eight years. Another adjustment on the QALE is the shortterm morbidity (STM). This is affected by things such as postoperative complications which prolong
hospital stay or otherwise adversely affect treatment outcome but are completely reversible--as opposed to irreversible outcomes which permanently lower QMs. The STM is merely subtracted from the LE to determine its effect on the QALE. Because the effects of the various components used to determine the QALE vary, sensitivity analysis is used to determine these effects. In sensitivity analysis a particular component of the decision tree, e.g., complication rate, is varied while other components are held constant. In this way, we can determine the effects of a high complication rate versus a low complication rate on the QALE. The LEs, QMs and STMs used in this decision analysis were determined from the literature on the treatment of AAA, colorectal carcinoma, and coexistent diseases [1-5, 9-27].
RESULTS Figure I depicts the choices available to the surgeon treating a patient with coexisting colorectal cancer and an AAA. An aortic aneurysm will be defined as one with aortic dilation greater than 4 cm. The first option, to do nothing for either disease, would only be considered for those patients with other end-stage illnesses or so severely diseased that they would be expected to die within a few weeks. This option will not be addressed in this study. The second option, resection of the AAA with no surgical therapy for the carcinoma, would only be considered in patients with very large symptomatic aneurysms and widely disseminated
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No 5 - 1991
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CONCOMITANT AAA AND COLORECTAL CANCER
metastatic cancer. This option also will not be subject to decision analysis. There are six issues involved when deciding the course of action in a patient with AAA and colon carcinoma: (I) L E after resection of the AAA: (2) LE after resection of the carcinoma; (3) chance of rupture of the AAA after resection of the carcinoma but prior to repair of the AAA; (4) chance of graft infection of an AAA repair after carcinoma resection; (5) chance of a carcinoma-related complication (i.e., obstruction or perforation) after a AAA repair but prior to carcinoma resection; and (6) operative mortality. After AAA repair LE essentially becomes age, sex, race and disease-specific for persons without AAA [9,26]. Therefore, the limiting LE for these patients is related to the carcinoma. Figures 2 to 5 represent the decision outcomes of the treatment options presented. Figure 2 shows the possible clinical outcomes of a patient who undergoes a resection of his colon cancer with nothing done about his AAA. The Q A L E of this decision is 5.82 years. Although the Dukes classification is the standard prognostic index, the Dukes classification of any particular patient prior to resection is unknown; therefore, the L E used in this decision analysis is estimated from the overall five-year survival reported in the literature [ 13,15,17]. Estimates of the probability of AAA rupture after resection of the carcinoma are estimated from reported rates [1,2,5,12,14] based on an eight week recovery period between operations. No data exist pertaining to the rate of known colorectal cancer obstruction or perforation. Indeed the accumulation of such data would be unethical since the standard of practice requires that colorectal cancers be resected in an expedient manner. It can be assumed that small colorectal cancer lesions would be at low risk and large or circumferential lesions would be at high risk. The rate of 10% used in Figure 2 is an estimate; therefore, particular attention to the sensitivity analysis of this component of the decision analysis is extremely important. Similarly, the rate of graft infection in patients who have recently undergone colorectal surgery is unknown--primarily because the fear of graft infection from bowel contaminants is so high that surgeons in general wait several weeks to months after colorectal surgery to proceed with AAA surgery [5]. The percentages used in Figures 3 and 4 are also estimates, so there is increased importance on the sensitivity analysis. Short-term morbidity is based on the rates and types of complications seen in these procedures [3,6,11,13,15, 17,19-21,23,26]. Appropriate estimates based on the literature were used for obstructing or perforating carcinomas [ 15,16,18,25,27]. Figure 3 shows the possible outcomes of a patient who undergoes a resection of his colon carcinoma, followed by repair of his AAA eight weeks later. The Q A L E is 6.13 years. His Q A L E depends on the aneurysm rupture rate for this eight week period
Uncompl Surgery icated < 71%
/ Complicated < (~ ~ Surgery 5%,STM=0.03yrs
NoAAARupture II 66.2% AAARupture < 33.8% NoAAARupturc II 66.2% AAARupture < 33.8%
Death FromSurgery 11 4%
Repair 50% Death II 50% Repair II 50% Death II 50%
Fig. 2. Outcome if cancer is resected and nothing done for aneurysm. Quality multiplier for those who survive is 0.97, for death is 0. Seventy-one percent of patients will have uncomplicated surgery; 25% will have complicated surgery with short-term morbidity of 10 days; 4% will die from the procedure; 66.2% will not rupture their aneurysms, while 33.8% will. Of those that rupture, 50% will die. Overall quality-adjusted life expectancy is 5.82 years.
and the risk of graft infection after large bowel surgery. For AAA of 4-5 cm, the estimated probability of rupture is 2.4% over eight weeks; for those 5 cm, it is 10.7% [1,2,5,22,24]. We may assume the consequences of a graft infection are a 10% mortality either secondary to sepsis or reoperation. See Table I for the results of the sensitivity analysis. Figure 4 represents the possible outcomes of repairing the AAA first, followed by resection of the cancer eight weeks later. The Q A L E is 6.02 years. This depends on the rate of perforation or obstruction for the carcinoma, which substantially increases the morbidity and mortality of a colonic resection [16,18,25,27]. The Q A L E is higher for the choice of AAA resection first when the aneurysm is TABLE I.--Sensitivity analysis Operation Resection of Ca first, followed by AAA repair (Fig. 4) Repair AAA first, followed by Ca resection (Fig. 2) Combined resection AAA and Ca (Fig. 5) QALE = Quality-adjusted a b d o m i n a l aortic a n e u r y s m
Parameters AAA < 5 cm AAA > 5 cm Graft infection 0% Graft infection 100% Ca complication 0% Ca complication 100% Operative mortality 5% Operative mortality 35% Graft infection 0% Graft infection 100%
life e x p e c t a n c y ;
Ca -
Colon carcinoma;
QALE 6.21 5.61 6.15 5.27 6.37 2.85 6.76 4.48 6.44 5.72 AAA
=
452
ANNALSOF VASCULARSURGERY
C O N C O M I T A N T AAA A N D COLORECTAL CANCER
Uncomplicated AAA Resection
Uneventful ~ Recovery 94.8%
[]
65% ComplicatedAAAResection 30%, Sa'M 008 yr II Death 5%
II
Uncomplicated Resection
71% SurgicalRepair 50%
II
Death 50%
II
Aortic Rupture 5.2%
Uncomplicated AAA Resection
]]
65% I
Uneventful Recovery 94.8%
Complicated AAA Resection
[[
30%,STM0.08yr Death 5%
II
Complicated Resection
25%,STM0.03yr SurgicalRepair 50%
[I
Death 50%
II
Rupture 5.2%
Death
.[I
4% Fig. 3. Outcome for resection of cancer first, followed by repair of aneurysm eight weeks later. Quality multiplier for survival is 0.96, for death O. Patients with an uneventful recovery after colon surgery number 94.8%; 5.2% will have aneurysmal rupture. Of those with uneventful recovery, 65% will have uncomplicated abdominal aortic aneurysm repairs, 30% complicated repair, and 5% will die perioperativety. Overall qualityadjusted life expectancy is 6.13 years.
4-5 cm and the carcinoma has a 5 cm, the QALE is higher for AAA resection first if the carcinoma has less than a 22% chance of obstructing or perforating (see Table I).
Figure 5 shows the outcomes of repairing the AAA and resecting the carcinoma during the same operation. The QALE is 6.20 years. This is dependent on the operative mortality of this combined procedure and the graft infection rate (see Table I).
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CONCOMITANT AAA A N D COLORECTAL CANCER
453
Uncomplicated Ca Resection I I 71% Uneventful Recovery
Complicated Ca Resection
90%
25%, STM 0.03 yr
Death
I[
4%
II
Emergency Resection Uncomplicated
[[
Uncomplicated Resection 80%
57% Complication
Emergency Resection Complicated
10%
30%, STM 0.06 yr
II
Death
13%
II
Uncomplicated Ca Resection ] ] 71%
Recovery
Complicated Ca Resection
90%
25%, S T . 0.o3 yr
II
Death 4~
II
Emergency Resection Uncomplicated
1]
Complicated Resection 15%. STM 0.03 yr
57%
Death
Ca Complication
Emergency Resection Complicated
10%
30%, STM 0.06 yr
II II
Death
II
13%
5%
Fig. 4. Outcome for resection of aneurysm first, followed by resection of cancer. Quality multiplier for survival is 0.97, and for death 0. Eighty percent of patients will have uncomplicated abdominal aortic aneurysm (AAA) repairs; 15% will have complicated repairs; 5% will die perioperatively. Of patients who survive AAA repair, 90% will recover without carcinoma-related complications, and 10% will have carcinoma-related complications. Of these patients with cancer-related complications, 57% will have uncomplicated emergency resections, 30% complicated emergency resections, and 13% perioperative death. Overall quality-adjusted life expectancy is 6.02 years.
454
C O N C O M I T A N T AAA A N D COLORECTAL CANCER
DISCUSSION Decision analysis helps quantitate the most probable outcomes of therapeutic choices. It is especially helpful in those clinical problems for which a definitive, controlled clinical trial has not been done. Decision analysis considers all possible outcomes, makes explicit all the assumptions about a clinical problem, and considers the quality of these outcomes [8]. Although decision analysis has been resisted by some physicians because it supposedly takes the art out of medicine, it is very similar to the algorithms of clinical choices published on a variety of disease diagnoses and therapies, except that the familiar concept of life expectancy, therapeutic morbidity and mortality, and quality of life are explicit and quantified. These advantages make decision analysis an excellent tool for determining the best treatment options for patients with concomitant A A A and colorectal cancer. The essential features that determine the priority of treatment in a patient with coexisting A A A and colorectal carcinoma are the aneurysmal rupture rate, rate of graft infection, and rate of cancerassociated complications. The rupture rate of aneurysms is related to their size [19,21]. In addition, laparotomy itself may increase the chance of rupture [14]. Reported rates of this complication vary between 0 and 30% [1,3,4,8,10]. The average of these reported rates standardized for an eight week period was used in this study. By sensitivity analysis, the QALE with a rupture rate of 0 would be 6.28 years and with a rupture rate of 23%, 5.60 years. Since the chance of rupture also depends on the size of the aneurysm, sensitivity analysis showed that AAAs 4-5 cm in diameter had a 2.4% chance of rupture while those >5 cm had a 10.7% chance. This had a significant effect on the QALE of patients who were operated upon for colon carcinoma first. Therefore, the size of the AAA as well as prior laporotomy had significant influence on the rate of AAA rupture. Graft infection after AAA repair is a devastating UncomplicatedResection
II
60% Complicated Resection
I[
30%, STM 0.08 yr Death
10%
II
Fig. 5. Outcome for resection of both aneurysm and cancer, simultaneously. Quality multiplier for survival is 0.96, for death 0. Overall quality-adjusted life expectancy is 6.20 years.
ANNALS OF VASCULAR SURGERY
complication. Although some feel that combining AAA repair with other gastrointestinal procedures is a safe and acceptable practice [10], others recommend that gastrointestinal operations should be avoided during aortic surgery [5]. There are no reported data on the incidence of aortic graft infection, either with concomitant colorectal surgery or shortly following or preceding colorectal surgery. For the decision tree depicted in Figure 3 (resection of colon carcinoma first, followed by repair of AAA), a 0% infection rate would yield a QALE of 6.15 years and a 100% rate, 5.77 years. There is a similar drop in the QALE from 6.44 years to 5.72 years when concomitant resections are performed. Individual surgeons and institutions may have their own experience or judgment as to what the graft infection rate would be and would be able to use their figures to determine the most appropriate treatment options using the data presented here. Although the rate of cancer-related complications is important in determining the QALE, how to determine this probability in the clinical setting is problematic. Most asymptomatic colorectal cancers can be inspected by proctoscopy or colonoscopy. This may help the surgeon determine if the lesion is at low risk for obstruction or perforation (i.e., 5% chance) or at high risk (i.e., >25% chance). For example, small lesions may be considered at low risk, while large, circumferential lesions may be considered at high risk. Raftery and Samson [15] have correlated the presenting symptoms of colorectal cancer with survival. Perforation and obstruction were poor prognostic signs, in addition to pain, weight loss and abdominal mass. This information may also be of benefit to the surgeon in determining the patient's chances of developing carcinoma-related complications. Colorectal carcinomas that lead to obstruction or perforation are very aggressive tumors and carry much worse prognoses than those that do not cause complications, and these complicated tumors are associated with higher operative morbidity and mortality [16,18,25,27]. However, recognition of those cancers at risk for impending complications will sway the surgeon to resection of the carcinoma prior to the AAA. Decision analysis, like clinical judgment, is only as good as the information available. Not enough information is available on the natural history or therapeutic results for patients who have coexisting AAA and colorectal carcinoma. Estimates from the literature can be made for AAA rupture. However, aortic graft infection rates and carcinoma obstruction and perforation rates are almost entirely unknown. When reviewing the decision trees and sensitivity analyses of this decision analysis, the reader is encouraged to recall his or her own experience with graft infections and carcinomarelated complications. Although these uncertainties
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CONCOMITANT AAA A N D COLORECTAL CANCER
p o s e limitations to the decision analysis presented, this is no different than the limitations imposed on nonquantitative clinical judgment and serves to e m p h a s i z e those areas of ignorance we have with regard to the clinical problem of coexisting A A A and colorectal cancer.
CONCLUSIONS In conclusion, concomitant A A A and colorectal carcinoma is a difficult m a n a g e m e n t problem. In general, the symptomatic lesion should be treated first. W h e n both lesions are asymptomatic, a A A A < 5 cm should be resected first if the carcinoma has a < 5 % chance of b e c o m i n g complicated. If the A A A is > 5 cm, then it should be resected first, if the carcinoma has a < 2 0 - 2 5 % chance of becoming complicated. Simultaneous reactions may be considered if the A A A is > 5 cm and the carcinoma has a > 7 5 - 8 0 % chance o f obstruction or perforation. Individual surgeons must temper these r e c o m m e n dations based on their o w n success rate and complication rate with these operations.
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