Molecular characterization of colorectal tumors in young patients compared with older patients and impact on outcome.

Abstract

505 Background: The incidence of colorectal cancer (CRC) among young individuals is rising. The effect of an individual’s age on their tumor molecular profile is unknown. Methods: Molecular profiles of 4,821 tumors obtained from younger and older CRC patients (pts) were reviewed and correlated with pt outcome. Protein expression (IHC), gene amplification (ISH), sequencing (NGS and Sanger), and fragment analysis were performed. T and Fisher’s exact tests determined differences between age groups; Kaplan-Meier methodology estimated survival. Results: Tumors from 1,277 younger (median age 40; range 15-45 yr) and 3,544 older (72; 65-98) pts were studied. Most frequently mutated genes included TP53, APC, KRAS, PIK3CA, SMAD4, and BRCA1/2. Mutation rates for BRAF (14.4% vs. 4.8%, p < 0.001), APC (62% vs. 54%, p = 0.0034), FBXW7 (9.6% vs. 5.5%, p = 0.01), and KRAS (45% vs. 41%, p = 0.02) were higher in older pts; NRAS mutation rates (4.5% vs. 3.9%) were similar in both groups. Younger pts had higher overexpression rates of HER-2/neu (3.2% vs. 1.8%, p = 0.017) and MGMT (64% vs. 58%, p = 0.001). Microsatellite instability (MSI), determined by IHC (MLH1, MSH2, MLH6 and PMS2) and fragment analysis, was similar between cohorts (10.3% vs. 8.1%), but somatic MSI high (determined by concurrent BRAF mutation) was higher in older pts (6% vs. 0%, p < 0.0001). There was no difference in TS (37% vs. 34%), ERCC1 (25% vs. 26%) or TOPO1 (49% vs. 46%) expression between age groups. Older pts showed a trend toward higher PD-L1 expression (2.9% vs. 0.7%, p = 0.0512) but there was no difference in the frequency of PD-1 expression on tumor-infiltrating lymphocytes (39% vs. 43%). Outcome was evaluable for 82 pts (younger, 47; older, 35). Most pts received FOLFOX + Bev as first line Rx. Median OS was worse in younger pts (p = 0.03). Low ERCC1 expression was associated with prolonged survival in older (p < 0.01) but not in younger (p = 0.3) pts. There was no association between TOPO1 expression and OS (p = 0.8). Pts with low TS expression showed a trend toward longer OS (p = 0.08). Conclusions: Young pts with CRC may carry genetic alterations that are distinct from older pts. A better understanding of disease biology may help to identify therapeutic targets for younger pts.