Merck & Co has filed its immunotherapy Keytruda in the US as a potential therapy for previously treated patients with advanced microsatellite instability-high (MSI-H) cancer.

Microsatellite instability - or MSI - is caused by a deficiency in the cell's ability to repair errors in the DNA sequence that occur during cell division leading to a characteristic change in microsatellite repeats. MSI-H is already an established biomarker in certain types of cancer.

"The FDA's acceptance of this application represents an important advance for the field of immuno-oncology and is further evidence of Merck's commitment to identifying patients most likely to benefit from Keytruda treatment," said Dr Roger M. Perlmutter, president, Merck Research Laboratories. 

"We believe that patients whose tumours harbour DNA repair defects may be especially responsive to Keytruda, and we look forward to working with the FDA to bring this important new therapy to these very challenging treatment situations."

The US Food and Drug Administration is reviewing the drug under its Accelerated Approval programme based on tumour response rate and durability of response, and has assigned the submission a priority review, which means that the company should have a decision by March 8.

The regulator also recently granted Breakthrough Therapy Designation to the for unresectable or metastatic MSI-H non-colorectal cancer, and previously granted it for the treatment of patients with unresectable or metastatic MSI-H colorectal cancer.

Keytruda is currently licensed for indications within melanoma, lung cancer and head and neck cancer.