Combination therapy of bevacizumab with either S-1 and irinotecan or mFOLFOX6/CapeOX as first-line treatment of metastatic colorectal cancer (TRICOLORE): Exploratory analysis of RAS status and primary tumour location in a randomised, open-label, phase III, non-inferiority trial

TP53 Gain-of-Function Mutation is a Poor Prognostic Factor in High-Methylated Metastatic Colorectal Cancer

BACKGROUND

Neither TP53 mutation nor DNA methylation status has been established as a biomarker alone of metastatic colorectal cancer. We analyzed the association between TP53 mutation functional subtypes and genome-wide DNA methylation status (GWMS) as combined prognostic markers.

METHODS

Patient clinical data were obtained from the TRICOLORE study, a randomized phase III trial. The TP53 mutations were classified into wild-type, gain-of-function (GOF) mutations, and non-gain-of-function (non-GOF) mutations. GWMS of the tumor tissues classified them into high-methylated colorectal cancer (HMCC) and low-methylated colorectal cancer (LMCC). Overall survival (OS) was compared based on these subgroups.

RESULTS

Of the 209 patients, 60 (28.7%) were HMCC and 149 (71.3%) were LMCC, 35 (16.7%) were TP53 wild-type and 174 (83.3%) were TP53 mutants including 79 (45.4%) GOF mutations and 95 (54.6%) non-GOF mutations. The OS of the HMCC group was shorter than that of the LMCC group (median 25.3 vs. 40.3 months, P < .001, hazard ratio 1.87) in the total cohort. The combined subgroup analyses of GWMS and TP53 mutation subtypes showed that the HMCC/GOF group had significantly shorter OS than the HMCC/non-GOF group, the LMCC/GOF group, and the LMCC/non-GOF group (median 17.7; 35.3, 40.3, and 41.2 months, P = .007, P < .001, and P < .001, respectively), regardless of the primary tumor location. By the multivariate analysis, only HMCC (P = .009) was a poor prognostic factor in the GOF mutation group.

CONCLUSIONS

TP53 GOF with HMCC is a newly identified poorest prognostic molecular subset in metastatic colorectal cancer.

A modified MethyLight assay predicts the clinical outcomes of anti-EGFR treatment in metastatic colorectal cancer

DNA methylation status correlates with clinical outcomes of anti‐epidermal growth factor receptor (EGFR) treatment. There is a strong need to develop a simple assay for measuring DNA methylation status for the clinical application of drug selection based on it. In this study, we collected data from 186 patients with metastatic colorectal cancer (mCRC) who had previously received anti‐EGFR treatment. We modified MethyLite to develop a novel assay to classify patients as having highly methylated colorectal cancer (HMCC) or low‐methylated colorectal cancer (LMCC) based on the methylation status of 16 CpG sites of tumor‐derived genomic DNA in the development cohort (n = 30). Clinical outcomes were then compared between the HMCC and LMCC groups in the validation cohort (n = 156). The results showed that HMCC had a significantly worse response rate (4.2% vs 33.3%; P = .004), progression‐free survival (median: 2.5 vs 6.6 mo, P < .001, hazard ratio [HR] = 0.22), and overall survival (median: 5.6 vs 15.5 mo, P < .001, HR = 0.23) than did LMCC in patients with RAS wild‐type mCRC who were refractory or intolerable to oxaliplatin‐ and irinotecan‐based chemotherapy (n = 101). The DNA methylation status was an independent predictive factor and a more accurate biomarker than was the primary site of anti‐EGFR treatment. In conclusion, our novel DNA methylation measurement assay based on MethyLight was simple and useful, suggesting its implementation as a complementary diagnostic tool in a clinical setting.