MTHFR and colorectal carcinoma: However, interestingly, data indicated that the MTHFR C667T polymorphism affected the prognosis of patients with CRC who were treated with chemotherapeutic drugs including pemetrexed and 5-fluorouracil (52, 53), suggesting that the impaired the folic acid metabolic pathway may affect the sensitivity to chemotherapy drugs and consequent prognostic events.