GlaxoSmithKline’s (NYSE: GSK) combination of two experimental melanoma medicines slowed the cancer’s progress longer than a single-drug treatment, a study found.

Patients taking Glaxo’s dabrafenib and trametinib together delayed tumors from progressing for 9.4 months, compared with 5.8 months for patients taking dabrafenib alone, according to the study of 162 patients. The trial was part of the second of three phases of human testing usually required by regulators.

Dabrafenib works by blocking BRAF, a mutant gene that spurs cancer-cell growth in about half of melanoma patients, while trametinib thwarts a related protein called MEK, which helps tumors resist an assault on BRAF. The study, funded by London- based Glaxo, was released today at the European Society for Medical Oncology meeting in Vienna and simultaneously published in the New England Journal of Medicine.

“The BRAFi/MEKi combo will attain a dominant position in the BRAF-mutant melanoma setting,” Andrew Baum, an analyst at Citigroup Inc. in London, said in a report earlier this week.

The company has begun a late-stage study of the combination therapy. On Aug. 3, Glaxo said it submitted the medicines individually to regulators in the U.S. and Europe for approval. If cleared for marketing, they would compete with Roche Holding AG’s Zelboraf, a targeted therapy approved last year for sale in the U.S.

The study tested two doses of trametinib. Among patients who received both drugs at the higher dose, 41 percent hadn’t progressed 12 months after treatment began, compared with 9 percent in the single-drug arm of the study.

Side Effects

An early-stage study presented in May suggested adding the MEK drug may reduce a signature side effect of BRAF drugs like Zelboraf — the development of non-melanoma skin cancer.

About 15 to 30 percent of melanoma patients treated with Zelboraf and other BRAF inhibitors develop non-melanoma skin cancers, scientists at the Institute of Cancer Research said in an article published in the New England Journal of Medicine in January. The drugs speed a type of skin malignancy known as squamous-cell carcinoma in patients who may have developed the cancer anyway, they said.
In the study presented today, squamous-cell carcinoma was seen in 7 percent of patients taking the higher dose two-drug combination and 2 percent in the lower dose, compared with 19 percent in the single-therapy group.

Separately, Roche said its early-stage study of Zelboraf combined with the MEK-inhibitor GDC-0973 can be safely delivered. The study did not evaluate efficacy.

Melanoma will strike more than 76,000 Americans this year, according to estimates from the National Cancer Institute. While patients with early stage disease respond well to treatment, the five-year survival rate for those with cancer that has spread is about 15 percent, according to the American Cancer Society.

GSK operates its North American headquarters in RTP.