Genomic Landscapes of Early-Onset Versus Average-Onset Colorectal Cancer Populations.

Background: Rates of early-onset colorectal cancer (eoCRC), defined as disease diagnosed at <50 years of age, are increasing. The incidence and spectrum of somatic and pathogenic germline variants (PGV) in this population are not well understood.

Methods: This cross-sectional study leveraged Tempus' clinicogenomic database, including de-identified records of patients diagnosed with CRC between 2000-2022, to analyze and compare eoCRC and average-onset colorectal cancer (aoCRC, disease diagnosed ≥50 years of age) patients. The frequency and spectrum of somatic mutations and PGVs in patients with eoCRC and aoCRC were evaluated and compared.

Results: Among 11,006 participants in this study, 57% were male, 76% were white, and 80% had stage 4 disease. Within the total cohort, 2379 had eoCRC and 8627 had aoCRC. Among patients with eoCRC, 4.2% had a tumor with high microsatellite instability and/or deficient mismatch repair (MSI-H/dMMR) and 6.8% with aoCRC had an MSI-H/dMMR tumor ( < 0.001). The most frequent somatic mutations involved , , and , with the most significant difference in , which was more frequently mutated in aoCRC (9.8% vs. 4.7%, < 0.0001). In total, 1413 (59.4%) eoCRC and 4898 (56.8%) aoCRC patients had matched normal specimen (blood or saliva) sequencing and a PGV was identified in 6.9% of eoCRC and 5.0% of aoCRC patients.

Conclusions: Somatic and germline mutation profiles were similar for eoCRC and aoCRC patients and may not adequately explain differences in tumor behavior and age of disease onset.