A new cancer drug called Keytruda (pembrolizumab) that aims to treat tumors based on the genetic characteristics instead of the location in the body has been approved by the US Food and Drug Administration.

Merck's Keytruda, an immunotherapy, is indicated for patients who suffer from genetic glitches in so-called "mismatch repair" genes, which means that their cells do not fully fix DNA errors. This can not only trigger cancer but also make tumors susceptible to drugs like Keytruda.

The drug is the first line of treatment to be given if a patient is manifesting one of two relatively rare genetic abnormalities and if suffering from a solid tumor. Dubbed as a checkpoint inhibitor, Keytruda works by releasing the body's immune system to attack tumors.

However, the downside of the Merck-made immunotherapy is that not all patients appear to get the benefit of the drug, and the reasons are not yet clear. The new approval, on the other hand, is indicated for patients who have already exhausted traditional treatment options like chemotherapy.

But the use of Keytruda comes with a price. Although genetic exams to identify mismatch repair genes are widely available and cost between $300 and $600, Keytruda itself is worth about $150,000 per year.

"This is an important first for the cancer community," Richard Pazdur, acting director of FDA's Center for Drug Evaluation and Research of the Office of Hematology and Oncology Product, said. "We have now approved a drug based on a tumor's biomarker without regard to the tumor's original location."

Keytruda is a precision medicine, which is the idea of customizing medical treatments based on a person's genetic makeup. But cancer therapies currently approved aim to treat cancer based on its location instead. Keytruda was first approved to treat advanced skin cancer in 2014 and has a remarkable success record including saving the life of former US President Jimmy Carter.