The FDA on Monday approved a new cancer treatment in an unconventional way: not by tumor type, but rather by the genetic mutation the drug targets.

The drug, Vitrakvi , was developed by Loxo Oncology in partnership with pharma giant Bayer.

It's only the second time the FDA has approved a cancer drug's use based on a certain mutation rather than a particular tumor type.

The Food and Drug Administration on Monday took an unconventional approach to approving a new cancer drug.

The drug, Vitrakvi, was developed by Loxo Oncology. It's the company's first drug to get approved.

Loxo's approach is to develop drugs that act on cancerous genetic mutations rather than the type of cancer a person has. For example, Vitrakvi, has been tested in patients with lung, colon, breast and thyroid cancer among others.

The drug comes with a high price tag of $393,000 a year. Bayer said in a statement that there's between 2,500 and 3,000 new patients with this mutation a year. The company set a lower price of $132,000 a year for the liquid form used in pediatric cases. Bayer said it will offer financial assistance to help patients afford the drug, reducing the out-of-pocket cost to $20 a month for most patients.

"Today’s approval marks another step in an important shift toward treating cancers based on their tumor genetics rather than their site of origin in the body," FDA Commissioner Scott Gottlieb said in a news release Monday.

In 2017, the drugmaker struck a $1.5 billion deal with pharma giant Bayer to commercialize and develop two of Loxo's drugs, including Vitrakvi.

Targeting a genetic mutation instead of cancer type

Building a treatment that's specific to a genetic mutation is a new approach to treating cancer. Most companies develop treatments for specific types of cancer, like lung cancer or melanoma, and seek approval just for that one kind of tumor at first, before setting up more trials to see how the drug does in other types of cancer.

Scientists have seen genetic patterns across cancer types for years, but the topic started attracting more attention in 2013 after the discovery that endometrial cancer was genetically similar to forms of ovarian and breast cancer.

In May 2017, the FDA approved a drug based on genetics rather than tissue type for the first time, paving the way for others including Loxo.

Loxo's drug works in cancer patients with a mutation called a "TRK gene fusion."

The company had seen promising results in its human trials. In a recent presentation at the European Society for Medical Oncology, Loxo said that out of 109 patients, 81% had an overall response rate, meaning their tumors shrank. In 17% of the cases, the patients had a complete response, meaning their tumors went away entirely.

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