This week the U.S. Food and Drug Administration approved Mekinist (trametinib) in combination with Tafinlar (dabrafenib) to treat patients with advanced melanoma that is unresectable (cannot be removed by surgery) or metastatic (late-stage).
In May 2013, the FDA approved both drugs as single agents to treat patients with unresectable or metastatic melanoma. Melanoma is the most aggressive type of skin cancer and is the leading cause of death from skin disease. The National Cancer Institute estimated that 76,690 Americans would be diagnosed with melanoma and 9,480 would die from the disease in 2013.
Mekinist and Tafinlar are used to block signaling in different sites of the same molecular pathway that promotes cancer cell growth. They are specifically indicated as a combination therapy for patients with melanoma whose tumors express gene mutations called BRAF V600E and V600K. The BRAF protein is involved in the regulation of normal cell growth, but it is mutated in approximately half of melanomas arising from the skin.
“Mekinist and Tafinlar are the first drugs approved for combination treatment of melanoma,” said Richard Pazdur, M.D., director of the Office of Hematology and Oncology Products in the FDA's Center for Drug Evaluation and Research. “Their development for combination use is based on the strong understanding of the biological pathways of the disease. This approval illustrates the value of continuing to study drugs in combination for clinical development.”
The safety and effectiveness of Mekinist in combination with Tafinlar were demonstrated in a clinical trial of 162 participants with unresectable or metastatic melanoma with the BRAF V600E or V600K mutation, most of whom had not received prior therapy. Participants received either Mekinist in combination with Tafinlar or Tafinlar as a single agent until their melanoma progressed or side effects became intolerable.
Results showed that 76 percent of participants treated with Mekinist in combination with Tafinlar had their cancer shrink or disappear (objective response) that lasted an average of 10.5 months. In contrast, 54 percent of participants treated with Tafinlar as a single agent experienced objective responses that lasted an average of 5.6 months. Clinical trials are ongoing to determine whether Mekinist in combination with Tafinlar improves survival.
The most common side effects reported in participants receiving Mekinist in combination with Tafinlar included fever, chills, tiredness, rash, nausea, vomiting, diarrhea, abdominal pain, peripheral edema (swelling in the hands and feet), cough, headache, joint pain, night sweats, decreased appetite, constipation and muscle pain. During clinical testing, the incidence and severity of fever increased when Mekinist was used in combination with Tafinlar.
Serious side effects included bleeding, clot formation, heart failure, skin problems and eye problems. One of the serious side effects of Tafinlar—the development of a new squamous cell carcinoma of the skin—was reduced when the drug was used in combination with Mekinist; this is consistent with the biology of the effects of these two drugs on the targeted molecular pathway. The incidence of squamous cell carcinoma of the skin in this trial was 7 percent with the combination compared to 19 percent with single agent Tafinlar. Other clinically significant side effects include kidney injury.
Women of child bearing potential should be advised that Mekinist and Tafinlar can cause birth defects in a developing fetus. Men and women should also be advised that Mekinist and Tafinlar treatment may cause infertility.
The FDA approved the combination of Mekinist and Tafinlar under the agency's accelerated approval program, which allows the FDA to approve a drug to treat a serious disease based on clinical data showing that the drug has an effect on a surrogate endpoint that is reasonably likely to predict a clinical benefit to patients. This program provides earlier patient access to promising new drugs while the company conducts confirmatory clinical trials. The FDA also reviewed this combination of drugs under the agency's priority review because they demonstrated the potential to be a significant improvement in safety or effectiveness in the treatment of a serious condition.