The utility of Medicare claims data for measuring cancer stage

BACKGROUND, The validity of using claims data for measuring tumor stage, on e of he most important determinants of choice of therapy and longterm survi val, is unknown. OBJECTIVES. TO determine the relative accuracy of both inpatient and hospit al Outpatient Medicare claims for measuring the stage of disease of six com monly diagnosed cancers. RESEARCH DESIGN. Analysis of a database linking Surveillance, Epidemiology, and End Results (SEER) registry data and Medicare claims in patients aged 65 years with cancer, SUBJECTS. Three hundred twenty thousand, six hundred and thirty seven cases of invasive breast, colorectal, endometrial, lung, pancreatic, and prostat e cancers diagnosed between 1984 and 1993. MEASURES. Using SEER files as the "gold standard," concordance with Medicar e claims, as well as sensitivity and positive predictive value of coding fo r each stage was measured. RESULTS. Although Medicare data correctly categorized local, regional, and distant stage tumors in 97%, 33%, and 65%, respectively, the data substanti ally overestimated the proportion of localized tumors and underestimated th e rate of regional stage disease. The highest concordance was observed for breast and colorectal cancer, However, the sensitivity and positive predict ive values were never simultaneously 80% within one stage of a specific can cer. The accuracy of coding for stage in Outpatient files was inferior to i npatient data. CONCLUSIONS. With few exceptions, Medicare claims have limited utility as a measure of cancer stage. If: tumor registry data are not available, invest igators should consider the trade offs in sensitivity and predictive value when considering a study that will use claims data.