DIAGNOSTIC CERTAINTY AND POTENTIAL FOR MISCLASSIFICATION IN EXOCRINE PANCREATIC-CANCER

Whereas over the last decade epidemiologic studies on exocrine pancrea tic cancer (EPC) continued to show a remarkable heterogeneity in diagn ostic criteria applied to define caseness, the actual magnitude and co nsequences of misclassification remain largely unexplored. The objecti ves were: (1) to estimate the degree of certainty with which cases of EPC are diagnosed in the two participating hospitals (to this end a di agnostic certainty classification (DCC) was developed; (2) to test whe ther characteristics of cases differed by degree of diagnostic certain ty; and (3) to assess what influence different definitions of case mig ht have on risk estimates for tobacco and alcohol. All cases with a di scharge diagnosis of EPC who attended at the Hospital del Mar between 1980-90 and at the Hospital Son Dureta between 1983-90 were identified through their respective tumor registries, and their clinical records were reviewed. Only 52% of 140 cases were classified in the group wit h a higher probability of EPC (group H). Diagnostic certainty appeared somewhat greater among women (age-adjusted odds ratio [OR(a)] 1.60, p = 0.18). Group H showed a higher proportion of cases with an interval from first symptom to diagnosis less than or equal to 1 month (OR(a) = 2.38, p < 0.05) and the proportion of adenocarcinomas was slightly h igher than in less certain cases (group L) (p = 0.051). A radical trea tment was exclusively attempted in group H (p < 0.001). DCC cut-off po ints had a significant effect on the proportion of smokers and of alco hol drinkers, as well as on the percent of cases with pathological (cy tohistological) confirmation. The proportion of cases unlikely to be o f pancreatic origin in spite of having pathological confirmation was h igh enough to cause significant misclassification bias. Because past e xposure to certain risk factors may differ among cases with different diagnostic certainty, we suggest to initially include in the case grou p patients who in spite of lacking pathological confirmation have stro ng clinical evidence supporting the diagnosis of EPC; subsequently, ri sk estimates should be computed across strata of diagnostic certainty to assess whether heterogeneity exists. In exocrine pancreatic cancer the impact of misclassification of disease status upon etiologic and p rognostic estimates deserves at least as much attention as misclassifi cation of exposure.