Patients with colorectal cancer associated with Lynch syndrome and MLH1 promoter hypermethylation have similar prognoses

Purpose: Mismatch repair deficient (dMMR) colorectal cancer (CRC) is caused by Lynch syndrome (LS) in 3% and sporadic inactivation of MEW by hypernaethylation (MLH1-hm) in 12% of cases. It is not clear whether outcomes between LS-associated and MLH1-hm CRC differ. The objective of this study was to explore differences in clinical factors and outcomes in these two groups. Methods: Patients with dMMR CRC identified by immunohistochemistry staining and treated at a single institution from 1998 to 2012 were included. MLH1-hm was established with BRAF mutational analysis or hypermethylation testing. Patients' charts were accessed for information on pathology, germ-line MMR mutation testing, and clinical course. Results:A total of 143 patients had CRC associated with LS (37 patients, 26%) or MLH1-hm (106 patients, 74%). Patients with LS were younger, more often male, presented more often with stage III disease, and had more metachronous disease than patients with MLH1-hm tumors. There was no difference in cancer-specific survival (CSS) between the groups; overall survival was longer in patients with LS, but this difference was minimal after adjusting for age and stage at diagnosis. Conclusion: CSS did not differ in LS-associated CRC compared with MLH1-hm CRC, suggesting that they carry a similar prognosis.