Purpose: Prognostic factors that could select high-risk recurrence colorectal cancer patients and predict chemosensitivity are needed. Since mutations of mitochondrial DNA (mtDNA) have been described in different types of cancers and since they may play a role in response to anticancer agents, we investigated in a population-based series of colorectal cancer patients the clinical value of mtDNA mutations.
Patients and methods: The displacement loop (D-loop) region of mtDNA was sequenced on a series of 365 patients recorded in the Digestive Cancer Registry of Côte-d'Or (France) between 1998 and 2000. Clinicopathologic characteristics were correlated to the presence of a D-loop mutation. Survival rates were compared with the log-rank test. A multivariate survival analysis was performed.
Results: D-loop mutations were found in 38.3% of the tumors. The 3-year survival rate was 53.5% in patients with D-loop mutation versus 62.1% in patients without (P = .05). After adjustment for age, stage, and microsatellite instability status, the relative risk of death in patients with D-loop mutation was 1.40 (95% CI, 1.02 to 1.93; P = .034) as compared with those without. In stage III colon cancers, adjuvant chemotherapy was beneficial only for patients without D-loop mutation (3-year survival, 78.3% v 45.4%, P < .02). In those with D-loop mutation who received adjuvant chemotherapy, the relative risk of death was 4.30 (95% CI, 1.23 to 15.00; P < .02).
Conclusion: The D-loop region is a hotspot for somatic mutations in colorectal tumors. Moreover, presence of tumor D-loop mutation appears to be a factor of poor prognosis in colorectal patients and a factor of resistance to fluorouracil-based adjuvant chemotherapy in stage III colon cancers.