Risk of late recurrence of colorectal and breast cancer among older long-term cancer survivors

BACKGROUND: A growing population of older adult cancer survivors faces competing cancer and noncancer health risks. There are limited real-world data on recurrence patterns beyond 5 years post-treatment. METHODS: This was a SEER-Medicare retrospective cohort study of patients aged ≥66 with stage I-III breast, colon, or rectal cancer who received definitive surgery and survived ≥5 years from diagnosis without recurrence or second primary malignancy. Late recurrence (5-10 years postdiagnosis) was identified using a validated algorithm to detect treated recurrence in Medicare claims. Demographic and clinical characteristics collected at cancer diagnosis were assessed as predictors of late treated recurrence using restricted mean survival time (RMST) regression. RESULTS: The sample included 12 859 breast, 17 329 colon, and 4427 rectal cancer survivors. The cumulative incidence of late treated recurrence 5-10 years postdiagnosis was 5.0% in breast, 4.4% in colon, and 8.0% in rectal cancer survivors. In all cohorts, stage was associated with shorter RMST. The absolute risk difference between stage I and III was greatest in breast (2% vs 18.1%), followed by rectal (5.2% vs 10.3%) and colon (2.7% vs 6.7%) cancer survivors (P < .001 for all cohorts). Although their effect on RMST was modest (