Learning from case reports: Diagnostic issues in an epidemiologic study ofpancreatic cancer

Epidemiologic studies on exocrine pancreatic cancer show a large heterogene ity in diagnostic criteria applied to define "caseness." Reanalyses conduct ed after review of diagnostic information have yielded substantially differ ent results than those based on more crude classifications of disease. Duri ng a multicenter prospective study on mutations in the K-ras gene in pancre atic and biliary diseases, hospital diagnoses from 602 patients were review ed by a panel of experts. There were two main motivations to do so: a gener ic interest for the quality of the diagnostic data, and the anticipation th at a firm diagnosis could be needed to assess whether patients whose tumors did not harbor the mutation were true negatives or false negatives. In add ition, the review of diagnoses was helpful to minimize tissue misclassifica tion, and it had a high educational value for clinicians and epidemiologist s. This article illustrates why and how this was so through a brief present ation of the 10 most significant cases. With respect to selection and class ification of subjects, the main issues that studies on pancreatic cancer ne ed to address are the differential diagnosis of exocrine pancreatic cancer and pancreatitis, the differential diagnosis of exocrine pancreatic cancer and other abdominal tumors, and the use of survival as a hallmark of pancre atic cancer. In epidemiologic studies of pancreatic cancer, it is warranted that a panel of experts centrally reviews all the existing diagnostic evid ence (cytohistological and other) of all patients, regardless of Whether th ey have cytohistological confirmation and of their hospital discharge diagn osis. J CLIN EPIDEMIOL 51;12:1215-1221, 1998. (C) 1998 Elsevier Science Inc .