Many new cancer drugs target genetic “biomarkers” that are specific to tumors — wherever in the body they may appear.

So on Tuesday, the U.S. Food and Drug Administration announced that, for the first time, it had approved a cancer drug based on disease genetics rather than the body part where the cancer originated.

The drug, Keytruda (pembrolizumab), is targeted to what are called “mismatch repair genes,” and its approval means it can be used to fight tumors with these genes wherever they appear — in the colon, pancreas, stomach, ovaries or other body sites.

“This is an important first for the cancer community,” Dr. Richard Pazdur, acting director of the Office of Hematology and Oncology Products in the FDA’s Center for Drug Evaluation and Research, said in an agency news release.

“Until now, the FDA has approved cancer treatments based on where in the body the cancer started — for example, lung or breast cancers,” said Pazdur, who also directs the FDA’s Oncology Center of Excellence. “We have now approved a drug based on a tumor’s biomarker without regard to the tumor’s original location.”

Keytruda, made by Merck & Co., targets tumors with DNA known as microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR). As the FDA explained, these gene abnormalities affect repair mechanisms inside the cell.

“Tumors with these biomarkers are most commonly found in colorectal, endometrial and gastrointestinal cancers, but also less commonly appear in cancers arising in the breast, prostate, bladder, thyroid gland and other places,” the FDA said in the news release. “Approximately 5 percent of patients with metastatic colorectal cancer have MSI-H or dMMR tumors.”

Keytruda works by targeting a cellular pathway that helps the body’s own immune system attack the cancer cells.

The drug had previously received separate approval for a variety of tumor types, such as metastatic non-small cell lung cancer, metastatic melanoma, and other cancers.

That approval has been widened and Keytruda is now allowed for the treatment of adults and children with certain tumors that can’t be surgically removed, or solid tumors that have spread.

The FDA said the drug is approved for use in two kinds of patients: Those who don’t have alternatives after tumors have progressed after treatment; and those with colorectal cancer that’s progressed after treatment with certain chemotherapy drugs.

The FDA said 149 patients with tumors with the biological variations — 15 tumor types in all — took part in five separate studies that led to the new approval. Tumors responded by either completely or partially shrinking in 40 percent of the patients. The findings also showed that more than three-quarters of those patients had a response for at least six months.

The drug has many side effects, including some that are serious — such as inflammation of healthy organs — so patients who experience those complications should stop taking the drug. Women who are pregnant or breast-feeding should not take the drug.

More information

There’s more on Keytruda at Cancer Research UK.

Source: HealthDay