High prevalence of deficient mismatch repair phenotype and the V600E BRAF mutation in elderly patients with colorectal cancer

Aims: Colorectal cancer (CRC) occurs mostly in the elderly. However, the biology of CRC in elderly has been poorly studied. This study examined the prevalence of deficient mismatch repair phenotype (dMMR) and BRAF mutations according to age.

Patients and methods: MMR phenotype was prospectively determined by molecular analysis in patients of all ages undergoing surgery for CRC. BRAF V600E mutation status was analysed in a subset of dMMR tumours.

Results: A total of 754 patients who underwent surgery between 2005 and 2008 were included in the study. Amongst them, 272 (36%) were ≥75years old. The proportion of women <75 was 38% and that ≥75 was 53% (p<0.0001). The prevalence of dMMR was 19.4% in patients ≥75 and 10.7% in patients <75 (p=0.0017). For patients ≥75, the prevalence of dMMR was significantly higher in women than in men (27% vs 10.2%, respectively; p=0.003) but was similar in women and men <75 (12.5% vs 9.7%, respectively; p=0.4). We examined BRAF mutation status in 80 patients with dMMR tumours. The V600E BRAF mutation was significantly more frequent in patients ≥75 than in patients <75 (72.2% vs 11.4%, respectively; p<0.001). In patients ≥75, there was no difference in the prevalence of the BRAF V600E mutation according to sex (78% in women and 70% in men, p=0.9).

Conclusions: The prevalence of dMMR in CRC is high in patients over 75. In elderly patients, dMMR tumours are significantly more frequent in women than in men. The BRAF mutation is frequent in elderly patients with CRC.