Effect of age on survival benefit of adjuvant chemotherapy in elderly stage III colon cancer patients: a population-based analysis

Abstract

4014 Background: Although sociodemographic disparities in colon cancer (CC) treatment (tx) have been documented, less attention has focused on age disparities. We estimated the modifying effect of age on the relationship between receipt of adjuvant chemotherapy (CH) and mortality among older patients with stage III CC. Methods: Medicare beneficiaries aged >66 years with stage III CC from 1997 to 2002 were identified in the Surveillance, Epidemiology and End Results cancer registries (SEER). Tx-related data were abstracted from linked Medicare claims. CH was defined as the receipt of 5-fluorouracil plus leucovorin, the recommended therapy during the study period, within 6 months of diagnosis. We used a continuous-time, interval-censored survival analysis with an interaction term to determine whether the effect of CH on hazard of CC-related death depends on age, controlling for sociodemographic and clinical factors, including proxy measures for performance status (PS). Results: 3,200 of the 6,711 stage III CC patients (48%) received CH. Increasing age was associated with a lower probability of receiving CH (78% of patients age 66–69 years versus 24% of patients age >80 years, p<0.01). Age significantly modified the survival benefit of CH (likelihood ratio test p<0.01). Compared to patients who did not receive CH, mortality was lower among patients who received CH across all ages, but the survival benefit of CH significantly decreased with increasing age [adjusted hazard ratios 0.37 (age 70 years) to 0.58 (90 years)]. Adjustment for sociodemographics, clinical factors and PS proxy measures attenuated but did not completely explain the effect modification of age on the relationship of tx and survival. Conclusion: Survival benefit of CH for CC was evident across all ages, however, most pronounced among ‘younger’ elderly. The modifying effect of age was not explained by sociodemographic or clinical factors. These findings have important clinical and policy implications for treatments among older cancer patients. Further study with newer, combination therapies and improved PS measures from claims will clarify the relationship between adjuvant treatment, age, and survival. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration sanofi-aventis sanofi-aventis Genentech™ BioOncology, sanofi-aventis sanofi-aventis