The US Food and Drug Administration will undertake a priority review of Bristol-Myers Squibb’s immunotherapy Opdivo as a treatment for patients with mismatch repair deficient (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (CRC).

dMMR occurs when the proteins that repair mismatch errors in DNA replication are missing or non-functional, which leads to MSI-H tumours in certain types of cancer, including CRC.

The company is seeking to expand the drug’s growing list of approvals to include its use in CRC patients whose disease is defined by these biomarkers and who have already had treatment with fluoropyrimidine-, oxaliplatin- and irinotecan-based chemotherapy.

Patients exhibiting dMMR or MSI-H colorectal cancer have a “distinct unmet need” as they are less likely to respond to conventional chemotherapy and have a shorter overall survival than those without these biomarkers, said Ian Waxman, development lead, Gastrointestinal Oncology, BMS.

Clinical data show that, at a median follow-up of 7.4 months, the overall response rate (ORR) in MSI-H CRC patients taking single-agent Opdivo was 31.1 percent, while median progression-free survival (PFS) was 9.6 months and the 12-month PFS rate was 48.4 percent.

In the US, CRC is the third most common cancer and the second leading cause of cancer-related deaths among men and women combined, with more than 134,000 new cases expected to be diagnosed annually; around 15 percent of CRC patients and 4-5 percent of metastatic CRC patients have dMMR or MSI-H biomarkers.