Abstract
Background/Aims Researchers are increasingly using diagnosis codes from administrative claims for cancer patients to identify metastatic disease at initial diagnosis or recurrence. The validity of metastasis codes on claims has not been established in population-based data. We used SEER cancer registry linked to Medicare claims to assess the completeness and validity of metastasis codes from Medicare claims for the four most common cancers in the U.S.
Methods The study included 127,453 breast, lung, prostate, and colorectal cancer patients newly diagnosed with localized, regional, or distant disease in the SEER data between January 1, 2005 and December 31, 2007. From Medicare claims, patients were classified as having regional or distant disease at diagnosis if they had one hospital claim with a metastasis code or two physician claims with metastasis codes on separate days within 3 months of diagnosis. Patients without claims with metastasis codes were classified as having local disease. We calculated sensitivity, specificity, positive and negative predictive values, and conducted multivariate logistic regression analysis to evaluate patient factors associated with stage misclassification for each cancer site.
Results For patients with distant disease per SEER data, the sensitivity and PPV of the claims was: breast (50.6%, 67.3%), colorectal (72.2%, 68.8%), and lung cancer (42.1%, 88.6%). None of the measures for stage simultaneously exceeded 80% for sensitivity, specificity, and positive predictive values for any of the cancer sites. In adjusted analysis, older, lower-income, and African American patients were more likely to have stage at diagnosis misclassified from Medicare claims.
Conclusions Use of diagnosis codes alone in Medicare claims will misclassify stage at diagnosis for cancer patients, particularly for patients with metastatic disease. Since cancer patients are likely to be evaluated most comprehensively at the time of diagnosis, our findings suggest that using diagnosis codes in Medicare claims to define recurrence will also be limited.
