Mismatch repair system deficiency as a resistance factor for locally advanced rectal cancer patients receiving neoadjuvant chemoradiotherapy

Available data on the impact of mismatch repair (MMR) system deficiency on tumor regression grade (TRG) among patients receiving neoadjuvant chemoradiotherapy (CRT) for locally advanced rectal cancer (LARC) are conflicting and derived from small studies. A retrospective study of 318 LARC patients receiving CRT in three centers in Italy evaluated the therapeutic implications of MMR status. The exploratory cohort consisted of 148 pMMR patients and 12 dMMR patients, while the validation cohort consisted of 146 pMMR patients and 12 dMMR patients. Major TRG was seen in 42.6% and 43.1% of pMMR patients in the two cohort versus no dMMR patients in both cohorts. The disease-free survival in the exploratory cohort and in the validation cohort were not reached versus 14 months and not reached versus 17 months, respectively. The authors conclude that these results indicated an association between dMMR and poor response to neoadjuvant CRT among LARC patients.