Extent of field change in colorectal cancers with BRAF mutation.

Introduction: Sporadic colorectal cancers with BRAF mutations constitute two distinct subgroups of colorectal cancers. Recent studies have linked the presence of the BRAF mutation to a familial inheritance pattern. This was a proof-of-concept study that aimed to examine: (a) the extent of field change in sporadic colorectal cancers with BRAF mutation; and (b) the extent of resection margins required and the pattern of DNA mismatch repair protein loss in these tumours.

Methods: Eight microsatellite instability-high tumours with positive BRAF mutation from an existing histopathological database were selected for BRAF mutation and mismatch repair protein analysis.

Results: All the resection margins were negative for BRAF mutation. Three tumours had loss of MLH1 and PMS2 expressions, and five tumours had no protein loss. Six peritumoral tissues were negative and one was positive for BRAF mutation.

Conclusion: The results suggest that any early field change effect is restricted to the immediate vicinity of the tumour and is not a pan-colonic phenomenon. Current guidelines on resection margins are adequate for BRAF mutation-positive colorectal cancers. Any suggestion of a hereditary link to these tumours is likely not related to germline BRAF gene mutations. The pattern of protein loss reinforces previous findings for the two subgroups of BRAF mutation-positive colorectal cancers.