Precision MedicinceThe US Food and Drug Administration (FDA) announced on Tuesday that they have approved an anti-cancer drug for use in patients with a specific biomarker. This is the first time the FDA has approved a cancer therapy based on a common biomarker instead of where in the body the tumour appears.

The drug, called Keytruda (pembrolizumab), can now be used to treat adult and paediatric patients with inoperable or metastatic solid tumours, provided they test positive for the biomarker. The biomarker itself arises from abnormalities within the DNA repair mechanisms of cancer cells, which are then known as microsatellite instability-high (MSI-H) or as mismatch repair deficient (dMMR). Patients who had progressed following prior treatments and have no suitable alternative treatments will be covered, as will colorectal cancer patients who have progressed following treatment with certain chemotherapy drugs.

MSI-H and dMMR tumours occur most commonly in colorectal, endometrial and gastrointestinal cancers, but they do also affect some patients with breast, bladder, thyroid, prostate, and other cancers. 5% of patients with metastatic colorectal cancer will develop a dMMR or MSI-H tumour.

Keytruda works by targeting the PD-1/PD-L1 pathway, encouraging the body’s immune system to attack the cancer cells (recent research into the pathway suggests that it might be a more effective target than we thought). The drug has previously been approved by the FDA for a selection of other cancers including metastatic non-small cell lung cancer and urothelial carcinoma.

This approval has been reached using the FDA’s Accelerated Approval pathway, which enables faster approval of drugs that can demonstrate the potential to benefit patients with an unmet medical need. The process examined the results of five clinical trials of the drug. Of the 147 patients involved in the trials, 39.6% of them displayed complete or partial shrinkage of their tumours and 78% of those had a response lasting six months or more.

“This is an important first for the cancer community,” said Richard Pazdur, M.D., Acting Director of the Office of Haematology and Oncology Products in the FDA’s Centre for Drug Evaluation and Research and Director of the FDA’s Oncology Centre of Excellence. “Until now, the FDA has approved cancer treatments based on where in the body the cancer started—for example, lung or breast cancers. We have now approved a drug based on a tumour’s biomarker without regard to the tumour’s original location.”