Comparison of Histopathologic Features of Right and Left Sided Colon Cancer.

INTRODUCTION

Colorectal cancer is one of the most common cancers in Aotearoa New Zealand. Evidence supports that right colon cancer (RCC) and left colon cancer (LCC) represent distinct entities, with RCC associated with a poorer prognosis, despite accounting for stage. Oncogenic mutations in MMR protein expression, BRAF V600E, and RAS genes have been shown to differ significantly between RCC and LCC, influencing tumour behaviour and prognosis.

METHODS

Histopathologic features of RCC and LCC in patients treated between 2018 and 2023 in a centre in Aotearoa New Zealand were evaluated. RCC was defined as arising from caecum to distal transverse colon, and LCC from splenic flexure to rectosigmoid junction. The primary outcomes were the rates of deficient MMR protein expression (dMMR), BRAF V600E, and NRAS gene mutations. Secondary outcomes included tumour characteristics, lymph node status, and AJCC prognostic stage.

RESULTS

A total of 376 patients were included, for a total of 390 tumours. RCC had a higher rate of dMMR tumours compared to LCC (50.4% vs. 13.75%; adjusted OR 6.36, 95% CI: 3.57-11.35). There were no significant differences in the rates of BRAF V600E or NRAS gene mutations between sides. RCC was more likely to be mucinous adenocarcinoma (23% RCC vs. 10% LCC; OR 2.99, 95% CI: 1.64-5.49), and to be high-grade (18.7% vs. 12.5%; OR 1.68, 95% CI: 1.03-2.92) compared to LCC.

CONCLUSION

RCC was associated with a higher rate of dMMR and high-grade tumours, and a greater proportion of mucinous adenocarcinomas.