Personalised cancer drug approved in US

For the first time, a drug for cancer based on a common biomarker rather than the location in the body where the tumour originated has been approved in the US.
The drug, Keytruda (pembrolizumab), now can be used for colon, pancreatic, stomach, ovarian, and other cancers if genetic testing reveals defects in so-called mismatch repair genes, researchers said.
The US Food and Drug Administration (FDA) granted accelerated approval to pembrolizumab for patients whose cancers have a specific genetic feature (biomarker).
This is the first time the agency has approved a cancer treatment based on a common biomarker rather than the location in the body where the tumour originated, FDA said.

Pembrolizumab is indicated for the treatment of adult and paediatric patients with unresectable or metastatic solid tumours that have been identified as having a biomarker referred to as microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR).
Experts at the Bloomberg-Kimmel Institute at Johns Hopkins University in the US designed the first clinical trial to test the theory that patients whose tumours have defects in mismatch repair genes may respond better to immunotherapy.

Tests for defects in mismatch repair are widely available and cost USD 300-600. Pembrolizumab can cost about USD 100,000 a year, fuelling the need to identify patients who are likely to respond to the drug.

First identified in 1993 by scientists, mistakes in mismatch repair genes are found in more than 4 per cent of cancers that occur each year in the US, including cancers of the colon, uterus, stomach, gall bladder, pancreas, ovaries, prostate, and small intestine.
The mutations disable cells' ability to repair errors in the DNA replication process, which triggers unchecked cellular growth, a hallmark of cancer.
Two decades later, an idea took root when experts found mismatch repair defects in a single patient with colon cancer who responded to immunotherapy while other patients with colon cancer did not.
Patients with tumours laden with mismatch repair defects have an abundance of abnormal proteins that look more "foreign" to immune system cells, triggering them to search for and destroy the unfamiliar-looking cancer cells.