The biology of early-onset colorectal cancer: An examination of tumor markers, pathology, and survival in a large cohort of patients.

3537 Background: Colorectal cancer (CRC) diagnosed before age 30 is a rare and often fatal disease whose biology remains poorly understood. To better understand its pathogenesis, we compared tumor markers, immunohistochemistry and clinical data in early-age onset and adult onset patients. Methods: In an international collaboration between academic centers in the United States and Australia, clinical data and archival tumor tissue were accrued for 94 patients treated surgically for early-age onset CRC (≤age 30). Cases were compared to 276 surgically treated adult onset CRC patients (≥age 50). Tumor tissue was assessed for morphology, microsatellite instability (MSI-H), microsatellite stability (MSS), Kras and Braf mutations, and expression of mismatch repair (MMR) proteins (MSH2, MLH1, MSH6, PMS2). Results: Early-age onset CRC was distinguished from adult onset CRC by poorer median disease-specific survival (44 vs. >120 mo, P<0.01), more advanced stage (III/IV) cancers (76% vs 50%, P<0.01), and higher prev...