Purpose:Wehypothesized that adverse prognostic associations of specific tumor molecular factors vary by patient age at colorectal cancer diagnosis. ExperimentalDesign:Weexamined the prognostic associations and interactions by age at colorectal cancer diagnosis (<60 vs. 60-74 vs. ≥75 years old) of key molecular factors-CpG island methylator phenotype (CIMP), microsatellite instability (MSI), KRAS, BRAF, and PIK3CA mutations, and nuclear CTNNB1 expression status-on colorectal cancer-specific survival (CSS) and overall survival (OS), using 1, 280 incident colorectal cancer cases (median age, 69 years; range, 38-91 years) within the Nurses' Health Study and Health Professionals Follow-up Study cohorts. Results: MSI-high was associated with better survival, whereas BRAF mutation was associated with worse survival, but these associations did not appreciably differ by age group. Status of CIMP, KRAS mutation, or PIK3CA mutation was not associated with prognosis regardless of age. Nuclear CTNNB1 expression was associated with a trend toward worse prognosis among older adults [age ≥ 75 years; multivariate HR, 1.67; 95% confidence interval (CI), 0.89-3.13 (for CSS); multivariate HR, 1.44; 95% CI, 0.93-2.24 (for OS)] but not among younger patients, and there was a statistically significant interaction by age (Pinteraction = 0.03 for CSS; Pinteraction = 0.007 for OS). Conclusions: Tumor nuclear CTNNB1 expression may be associated with higher mortality among older patients with colorectal cancer but not among younger patients. Our findings need to be confirmed in independent datasets. Detailed exploration of tumor molecular signatures in older patients with colorectal cancer in large populations is warranted. Clin Cancer Res; 22(6); 1489-98.
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