Yesterday, the US Food and Drug Administration (FDA) approved a new therapy for patients with advanced melanoma. The treatment, Keytruda (pembrolizumab), proved so successful in a large Phase 1 clinical trial that the drug was granted breakthrough therapy designation by the FDA, meaning that it was fast tracked for approval.
Melanoma is a type of cancer that begins in pigment-containing cells called melanocytes. Melanocytes are predominantly found in the skin but are also found in other areas such as the eye and the intestines.
Melanoma is less common than other types of skin cancer but it is the most serious. It accounts for approximately 5% of all new cancers in the US. According to the National Cancer Institute, it is estimated that over 76,000 US citizens will be diagnosed with melanoma this year and almost 10,000 will die.
The new therapy is an antibody that works by increasing the ability of immune cells to fight tumor cells. Specifically, Keytruda targets a molecule called programmed cell death 1 (PD-1) and prevents it from interacting with the molecules that naturally bind to it in the body. PD-1 has sparked interest in recent years because it has been suggested to play a critical role in tumor evasion from the immune system.
T cells are a type of white blood cell that, among other things, seek out and destroy tumor cells. PD-1 is a receptor found on activated T cells that negatively regulates the immune response by inhibiting T cell growth. PD-1 levels are increased in certain types of tumors, which is thought to not only decrease antitumor T cell proliferation, but also increase T cell death. Blocking the PD-1 receptor with an antibody in both tumor cells in the lab and mouse cancer models was found to potently inhibit tumor growth. Now, very positive results from a new clinical trial have demonstrated that this therapy has lived up to our high expectations.
The trial involved more than 600 patients who had melanoma that had spread to other parts of the body. Tumors shrank to some degree in 72% of the patients given Keytruda and 34% of patients showed an objective response, meaning their tumors shrank by more than 30% and did not re-grow. The drug is now being tested in ongoing Phase 2 and 3 clinical trials, again involving patients with advanced melanoma. While it has only been tested in melanoma patients, it is thought that it may also have potential in other cancers, such as lung and bladder cancer.
“The drug is a game changer, a very significant advance in the treatment of melanoma,” principal investigator Dr. Antoni Ribas said in a news-release. “For patients who have not responded to prior therapies, this drug now provides a very real chance to shrink their tumors and the hope of a lasting response to treatment.”
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