Modification of claims-based measures improves identification of comorbidities in non-elderly women undergoing mastectomy for breast cancer: a retrospective cohort study
BACKGROUND Comorbidity is an important prognostic factor for elderly patients with head and neck cancer. Investigators are faced with the dilemma of selecting the appropriate comorbidity instrument for outcomes research in cancer. The goal of this study was to compare 2 general comorbidity indices with 2 disease-specific indices. METHODS The Surveillance, Epidemiology, and End Results (SEER)-Medicare-linked database was used to identify 15,493 patients with incident squamous cell carcinomas of the oral cavity, pharynx, and larynx first diagnosed between December 1983 and December 1994. Comorbid ailments were identified through the use of the International Classification of Diseases, 9th edition codes in the Medicare inpatient and outpatient claims for 7131 patients. The overall severity of comorbidity was classified according to 2 general comorbidity indices: the Charlson Comorbidity Index and the Klabunde Index, and 2 disease-specific indices: the Washington University Head and Neck Index and the Head and Neck Cancer Index. Overall survival was the primary end point. Cox proportional hazards analysis was used to assess the performance and discrimination of the comorbidity indices. RESULTS For each of the 4 comorbidity indices, there was a weak trend of worse survival with higher levels of comorbidity. The 2 general indices performed as well as the 2 disease-specific indices and no instrument clearly performed better than the others. CONCLUSION Both the general and disease-specific comorbidity indices provided important prognostic information. The disease-specific indices did not perform better than the general indices. In this claims-based analysis, there was no apparent advantage to using a disease-specific index when attempting to predict overall survival.