Divergent oncogenic changes influence survival differences between colon and rectal adenocarcinomas

Area of Science:

• Oncology
• Molecular Biology
• Gastroenterology

Background:

• Colorectal cancers arise from distinct molecular mechanisms, including chromosomal instability, DNA mismatch repair deficiency (microsatellite instability), and CpG island methylator phenotype.
• Understanding the molecular disparities between colon and rectal cancers is crucial for accurate diagnosis and treatment strategies.

Purpose of the Study:

• To evaluate the differences in neoplastic changes and molecular profiles between colon and rectal adenocarcinomas.
• To compare the incidence of microsatellite instability, methylation, and specific gene mutations (KRAS, BRAF) in colon versus rectal cancers.
• To assess the impact of molecular phenotypes on clinical outcomes and survival across anatomic sites.

Main Methods:

• Analysis of a clinic-based colorectal frozen tumor bank.
• DNA extraction and molecular analysis for microsatellite instability, methylation, and KRAS/BRAF mutations.
• Comparison of patient demographics, tumor characteristics, and clinical outcomes between colon and rectal cancer cohorts.

Main Results:

• Colon cancers showed significantly higher rates of microsatellite instability (27% vs. 7%) and methylator phenotype (28% vs. 3%) compared to rectal cancers.
• BRAF mutations were more frequent in colon cancers (16.7% vs. 0%), while KRAS mutation rates were similar.
• Microsatellite stable tumors were associated with an increased risk of disease recurrence (OR, 3.86).

Conclusions:

• Colon cancers are molecularly heterogeneous, whereas rectal cancers predominantly follow a single neoplastic pathway.
• Molecular differences, including genetic and epigenetic alterations, are more influential on prognosis than anatomic location.
• Oncogenic pathways significantly contribute to survival differences observed between colon and rectal cancers.