Reginald

E. Greene,

MD

Missed Lung Nodules: for Cancer Cure’

I

this issue of Radiology, John Austin and his colleagues remind us of what radiologists have long recognized: Lung cancer nodules are commonly missed in prospect but easily seen in retrospect (1). These detection failures provide two important lessons. The first is that lung cancers often grow slowly enough to be radiographically detectable while they are still localized and asymptomatic. The second lesson is that we still poorly understand and fail to apply principles of psychophysics to help reduce our errors in perception (2). N

RADIOGRAPHIC INCIDENT

SCREENING LUNG CANCERS

FOR

Radiographic screening has not been endorsed as a potentially fruitful enterpnse to reduce lung cancer mortality (3). In fact, the results of a recent large randomized multicenter experiment in clinical screening, the Early Lung Cancer (ELC) trial, have largely been interpreted in negative terms (4,5). After gathering follow-up data for 10 years, the conductors of the ELC trial reported the same lung cancer mortality for both the study and control populations, concluding that screening programs of penodic sputum cytologic evaluation and chest radiography were of no value (6). Questions of economic outcomes and real patient benefit versus effects of antifactual screening (eg, selection bias, length bias, and lead-time effects) have been widely discussed. It is often overlooked, however, that the ELC trial was primarily designed to test sputum cytologic evaluation, not radiography. As a result, the design at

Index

als

terms:

#{149} Lung

nodule, Radiology

I

From

chusetts 02114.

Diagnostic

neoplasms,

radiology diagnosis,

#{149} Editon#{149}

60.321

Lung,

60.3221 1992;

the

182:8-9

Department

of Radiology,

Massa-

General Hospital, Fruit St, Boston, MA Received and revision requested September 3, 1991; revision received and accepted October 1 1 . Address reprint requests to the author. C RSNA, 1992 See also the article by Austin et al (pp 115122) in this issue.

8

Lost

Opportunities

two of the three centers contributing to the ELC trial incorporated radiographic screening into both the study and control arms of the trial. This design methodology greatly reduced the power to detect real reduction in mortality attributable to radiographic screening. Data from the sole center at which the effect of radiographic screening could be evaluated showed that radiography alone allowed the detection of six times as many lung cancers as sputum cytologic evaluation (7). Although the ELC trial showed no improvement in overall mortality in the study groups vis-#{224}-vis the control group, two anomalies in the data mdicated that (a) many more stage 1 cancers than expected were detected in both the control (25%) and study (35%) groups, and (b) 5-year mortality rates in both the control and study groups (35% each) were lower than those of other lung cancer studies (a 10% mortality was expected for the United States during those years for the same age distribution) (8). By using powerful case mortality analyses and merging the ELC trial data for all incident cancers detected with radiography or cytology (including adjustments for age, smoking history, and histologic cell type), Chu and Smart were able to attribute these two anomalies to the beneficial effects of radiographic screening in both the study and control arms of two of the three ELC trial centers (Chu KC, Smart CR, unpublished data, 1991). The reduction in mortality is attributable to chest radiography (P < .004) but not to sputum cytologic assessment, according to Chu and Smart. The results of this analysis suggest that screening radiography alone may reduce lung cancer mortality by 10%, or about 15,000 persons, in the United States annually. It is unfortunate that the design of the ELC trial did not provide the statistical power to carry out a more sensitive test of the effectiveness of screening radiography (9). It now finally appears, however, that the promising prospect of reducing lung cancer mortality with radiography will be tested specifically by the National Cancer Institute in a multiphasic screening trial possessing adequate power to show a 10% reduction in mortality attributable to radiography alone.

PSYCHOPHYSICS

AND

COMPUTER-AIDED

SCREENING

The full potential of radiographic screening cannot be realized unless new technologic advances are employed and the principles of psychophysics are applied to lesion detection. We must learn why a cancer lesion can be clearly recognized when the location is known, but go totally undetected in a prospective

search.

We

know

from

various

studies of observer performance that the characteristics of the final image display consistently affect the ability of a radiologist to detect subtle lung nodules (10). In computed digital radiography, we now have a powerful raw diagnostic tool of unprecedented power with which to apply psychophysical principles to the task of detecting subtle lung nodules. Digital technology can potentially improve screening by providing compatibility for computer-assisted detection of lesions and by permitting flexible manipulation of gray scale and edge enhancement of the images presented to the radiologist. Radiology has a long tradition of screening for occult disease, beginning with the first attempts to uncover asymptomatic tuberculosis in 1896. Abstinence from smoking and a cleanup of environmental pollutants are certainly the long-term answers to the reduction in deaths from lung cancer, but in the meantime, an increasingly large number of people with potentially treatable lung cancers continue to die. Lung cancer is now a more common cause of death than heart disease, and it is responsible for more deaths in men and women than any other cancer (11). If some fraction of the unprecedented energy mobilized for radiologic screening of breast cancer, the second leading cause of cancer death among women, were also directed at the most common cause of cancer death in both women and men, fewer lung cancer deaths might occur in the next generation. U

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#{149} 9