資料來源：https://www.reuters.com/article/us-merck-co-fda-idUSKBN18J2T9

Merck & Co's immunotherapy Keytruda on Tuesday became the first cancer drug ever approved by the U.S. Food and Drug Administration based on a patients' specific genetic traits, regardless of where in the body the disease originated.

The approval marks a major step in so-called precision medicine, where genetic biomarkers may determine the course of therapy rather than the type of cancer. The hope is that advanced genetic information will one day be able to identify which patients are most likely to benefit from a specific treatment.

"Until now, the FDA has approved cancer treatments based on where in the body the cancer started - for example, lung or breast cancers," said Richard Pazdur, head of oncology products for the FDA's Center for Drug Evaluation and Research.

The accelerated approval was for solid tumor cancers not eligible for surgery or that have spread in patients identified as having a biomarker called microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR).

Tumors with those traits are most common in colorectal, endometrial and gastrointestinal cancers, but may also appear in cancers of the breast, prostate, bladder, pancreas, thyroid gland and others.

Dr. Drew Pardoll, director of the Johns Hopkins Bloomberg-Kimmel Institute that designed and led the trial that led to the historic approval, called it "a marriage of cancer genetics and cancer immunology."

Patients whose tumors are laden with the genetic defect have an abundance of abnormal proteins that look more foreign to immune cells, triggering them to search out and destroy the cancer cells.

Keytruda belongs to a new class of drugs called PD-1 or PD-L1 inhibitors that block a mechanism tumors use to evade detection from cancer-fighting cells. There are now five such drugs available for a variety of cancers.

"This was one of those eureka trials where it didn't take a lot of patients to see this was going to be something major," Pardoll said in an interview.

He said about 4 percent of advanced cancers, or 15,000 to 20,000 cases each year in the United States, carry the genetic traits addressed in the approval.

Tests for the specific genetic defects are widely available, costing between $300 and $600.

The approval covers children and adults whose cancer has progressed despite prior treatment and those who have no satisfactory alternative treatment options, including patients whose colorectal cancer has progressed following chemotherapy.

The FDA grants accelerated approvals to drugs for serious conditions with unmet medical needs if the treatment appears to have effects deemed reasonably likely to predict a clinical benefit. Merck must still conduct studies to confirm the anticipated benefit.

The approval further solidifies Merck's leading position in the burgeoning field of treatments that help the immune system fight cancer, a mantle it seized last year when Keytruda extended survival as an initial treatment for advanced non-small cell lung cancer (NSCLC).

Keytruda was previously approved to treat advanced melanoma, advanced NSCLC, head and neck cancers and classical Hodgkin lymphoma. Last week it won U.S. approval for bladder cancer and is awaiting an FDA decision for gastric cancer.

(Additional reporting by Natalie Grover in Bengaluru; Editing by James Dalgleish and Diane Craft)