In what has been described as a significant step forward in the treatment of advanced melanoma, US regulators have approved a combination drug therapy to treat the most aggressive and dangerous form of skin cancer.

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The majority of skin cancers are caused by exposure to ultraviolet light.

The US Food and Drug Administration (FDA) have approved the addition of cobimetinib to vemurafenib to treat metastatic melanoma that has spread to other parts of the body or cannot be removed surgically and has a mutated BRAF gene.

Vemurafenib is marketed as Zelboraf and cobimetinib as Cotellic by Genentech of San Francisco, CA.

If melanoma is not diagnosed early, it is likely to spread to other parts of the body (metastasize). Around half of people with metastatic melanoma have a mutated BRAF gene.

The mutated gene – there are two forms, called BRAF V600E and BRAF V600K – can be detected with an FDA-approved test. The FDA say doctors should check their patients have one of these mutations – by testing a tumor specimen – before giving them the new drug combination.

Skin cancer is the most common cancer in the US. The majority of skin cancers are caused by exposure to ultraviolet (UV) light. While melanoma accounts for 1 in 50 cases of skin cancer, it causes the most deaths. Melanoma starts in melanocytes, the skin cells that make melanin – the pigment that gives skin its color.

The National Cancer Institute estimate that in 2015, nearly 74,000 people in the US will be diagnosed with melanoma and nearly 10,000 will die from the disease.

In Tuesday’s announcement, Dr. Richard Pazdur, director of the Office of Hematology and Oncology Products in the Center for Drug Evaluation and Research at the FDA, said:

Today’s approval provides a new targeted treatment that, when added to vemurafenib, demonstrates greater benefit than vemurafenib alone in patients with BRAF mutation-positive melanoma.”

On its own vemurafenib – which was recently approved by the FDA – does not completely block the signal that the mutated BRAF gives to makes the cancer keep growing. Cobimetinib works by blocking the activity of an enzyme known as MEK, which is active in another part of the same pathway.

A trial conducted at the University of California-Los Angeles (UCLA) and 135 other sites in the US, Europe, Australia and Russia showed that the combination of the two drugs slows the growth of melanoma.

Another benefit from adding cobimetinib is that it reduces the risk of secondary skin cancer that arises in 25% of patients taking vemurafenib alone.

The drug combination was tested in nearly 500 patients with the BRAF-mutated melanoma. All patients received vemurafenib and were then randomly selected to also take either cobimetinib or a placebo.

The results showed that on average, patients taking the combination of vemurafenib and cobimetinib experienced a delay in the time it took for symptoms to get worse, compared with those on vemurafenib plus placebo – about 12.3 months compared with 7.2 months after treatment began.

Also, patients taking the combination drug lived longer – about 65% of patients on vemurafenib and cobimetinib were alive 17 months after commencing treatment compared with half of those on vemurafenib plus placebo.

There was also a difference in effect on tumors; 70% of patients receiving both vemurafenib and cobimetinib saw their tumors shrink partially or completely, compared with around half of those in the vemurafenib plus placebo group.

Antoni Ribas, UCLA professor and senior investigator of the trial, says the FDA approval represents a significant advance in the treatment of metastatic melanoma, and:

For patients with a BRAF mutated melanoma, the combination has higher activity to shrink their tumors, and with less side effects than the drugs on their own.”

The most common side effects of the combined treatment are diarrhea, sensitivity to UV light, nausea, fever and vomiting.

Cobimetinib can also cause severe side effects, including damage to muscle in the heart and elsewhere, new skin tumors, retinal detachment, severe skin rash and liver damage.

People taking cobimetinib should avoid the sun and protect against sun exposure when outdoors – such as wear protective clothing and use broad-spectrum UVA/UVB sunscreen. The drug can harm a developing fetus, so women taking it should use effective contraception, say the FDA.

Meanwhile, Medical News Today recently learned of a twins study that found the number of moles on a person’s right arm can predict their risk of melanoma.