Mitochondrial DNA Copy Number as a Biomarker for Guiding Adjuvant Chemotherapy in Stages II and III Colorectal Cancer Patients with Mismatch Repair Deficiency: Seeking Benefits and Avoiding Harms

Abstract

Background: Colorectal cancer (CRC) patients with mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) status are conventionally perceived as unresponsive to adjuvant chemotherapy (ACT). The mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA copy number (mtDNA-CN) expression. In light of previous findings indicating that the frequent truncating-mutation of TFAM affects the chemotherapy resistance of MSI CRC cells, this study aimed to explore the potential of mtDNA-CN as a predictive biomarker for ACT efficacy in dMMR CRC patients.

Methods: Levels of MtDNA-CN were assessed using quantitative real-time polymerase chain reaction (qRT-PCR) in a cohort of 308 CRC patients with dMMR comprising 180 stage II and 128 stage III patients. Clinicopathologic and therapeutic data were collected. The study examined the association between mtDNA-CN levels and prognosis, as well as the impact of ACT benefit on dMMR CRC patients. Subgroup analyses were performed based mainly on tumor stage and mtDNA-CN level. Kaplan-Meier and Cox regression models were used to evaluate the effect of mtDNA-CN on disease-free survival (DFS) and overall survival (OS).

Results: A substantial reduction in mtDNA-CN expression was observed in tumor tissue, and higher mtDNA-CN levels were correlated with improved DFS (73.4% vs 85.7%; P = 0.0055) and OS (82.5% vs 90.3%; P = 0.0366) in dMMR CRC patients. Cox regression analysis identified high mtDNA-CN as an independent protective factor for DFS (hazard ratio [HR] 0.547; 95% confidence interval [CI] 0.321-0.934; P = 0.0270) and OS (HR 0.520; 95% CI 0.272-0.998; P = 0.0492). Notably, for dMMR CRC patients with elevated mtDNA-CN, ACT significantly improved DFS (74.6% vs 93.4%; P = 0.0015) and OS (81.0% vs 96.7%; P = 0.0017), including those with stage II or III disease.

Conclusions: The mtDNA-CN levels exhibited a correlation with the prognosis of stage II or III CRC patients with dMMR. Elevated mtDNA-CN emerges as a robust prognostic factor, indicating improved ACT outcomes for stages II and III CRC patients with dMMR. These findings suggest the potential utility of mtDNA-CN as a biomarker for guiding personalized ACT treatment in this population.

Keywords: Adjuvant chemotherapy; Colorectal cancer; Mismatch repair deficient; Mitochondrial DNA copy number.

Fig. 1

Research flow chart and mtDNA-CN characteristics of stages II and III CRC patients with dMMR. A Schematic diagram of research flow. B The distribution of mtDNA-CN in CRC cases. C The deficient mismatch repair proteins in 308 locally advanced colorectal cancer patients. D The mtDNA-CN ratio in tumor tissue versus non-tumor tissues cases. MtDNA-CN, mitochondrial DNA copy number; CRC, colorectal cancer; dMMR, deficient mismatch repair; IHC, immunohistochemistry; PMMR, mismatch repair-proficient; qPT-PCR, quantitative real-time polymerase chain reaction; ACT, adjuvant chemotherapy; T, tumor; N, non-cancerous

Fig. 2

Correlations between mtDNA-CN and clinicopathologic features in stages II and III CRC with dMMR. A Sex. B Age. C Tumor location. D Stage T. E Stage N. F CEA. G CA19-9. H Tumor differentiation. I Vascular invasion. J Nervous infiltration. K Tissue type. L KRAS status. M BRAF status. N NRAS status. O PIK3CA status. MtDNA-CN, mitochondrial DNA copy number; CRC, colorectal cancer; dMMR, deficient mismatch repair; CEA, carcinoembryonic antigen; CA 19-9, carbohydrate antigen 19-9; AC, adenocarcinoma; MC, mucinous adenocarcinoma; WT, wild type; MT, mutant type

Fig. 3

Correlation between ACT, mtDNA-CN and the prognosis of stages II and III CRC patients with dMMR. A Kaplan-Meier analysis of DFS based on mtDNA-CN in the CRC cohort. B Kaplan-Meier analysis of OS based on mtDNA-CN in the CRC cohort. C Kaplan-Meier analysis of DFS based on ACT in the CRC cohort. D Kaplan-Meier analysis of OS based on ACT in the CRC cohort. E Kaplan-Meier analysis of DFS based on ACT in the stage II CRC with dMMR cohort. F Kaplan-Meier analysis of OS based on ACT in the stage II CRC with dMMR cohort. G Kaplan-Meier analysis of DFS based on ACT in the stage III CRC with dMMR cohort. H Kaplan-Meier analysis of OS based on ACT in the stage III CRC with dMMR cohort. ACT, adjuvant chemotherapy; MtDNA-CN, mitochondrial DNA copy number; CRC, colorectal cancer; dMMR, deficient mismatch repair; DFS, disease-free survival; OS, overall survival

Fig. 4

A subgroup analysis of the correlation between ACT, mtDNA-CN, and the prognosis of stages II and III CRC patients with dMMR. A Kaplan-Meier analysis of DFS based on ACT in the low mtDNA-CN CRC cohort. B Kaplan-Meier analysis of OS based on ACT in the low mtDNA-CN CRC cohort. C Kaplan-Meier analysis of DFS based on ACT in the high mtDNA-CN CRC cohort. D Kaplan-Meier analysis of OS based on ACT in the high mtDNA-CN CRC cohort. E Kaplan-Meier analysis of DFS based on ACT in the stage II dMMR CRC with low mtDNA-CN cohort. F Kaplan-Meier analysis of OS based on ACT in the stage II dMMR CRC with low mtDNA-CN cohort. G Kaplan-Meier analysis of DFS based on ACT in the stage II dMMR CRC with high mtDNA-CN cohort. H Kaplan-Meier analysis of OS based on ACT in the stage II dMMR CRC with high mtDNA-CN cohort. I Kaplan-Meier analysis of DFS based on ACT in the stage III dMMR CRC with low mtDNA-CN cohort. J Kaplan-Meier analysis of OS based on ACT in the stage III dMMR CRC with low mtDNA-CN cohort. K Kaplan-Meier analysis of DFS based on ACT in the stage III dMMR CRC with high mtDNA-CN cohort. L Kaplan-Meier analysis of OS based on ACT in the stage III dMMR CRC with high mtDNA-CN cohort. ACT, adjuvant chemotherapy; MtDNA-CN, mitochondrial DNA copy number; CRC, colorectal cancer; dMMR, deficient mismatch repair; DFS, disease-free survival; OS, overall survival

Fig. 5

Efficacy of ACT on each clinicopathologic factor and mtDNA-CN for DFS and OS for stages II and III CRC patients with dMMR. ACT, adjuvant chemotherapy; MtDNA-CN, mitochondrial DNA copy number; DFS, disease-free survival; OS, overall survival; CRC, colorectal cancer; dMMR, deficient mismatch repair; CEA, carcinoembryonic antigen; CA 19-9, carbohydrate antigen 19-9