Patients on Vemurafenib Need Testing for RAS Mutations

Secondary Cancers a Concern

Nick Mulcahy

January 20, 2012

January 20, 2012 — Patients with advanced melanoma who are treated with vemurafenib (Zelboraf, Plexxikon/Roche) should be tested for RAS mutations, according to an editorial published in the January 19 issue of the New England Journal of Medicine.

A study that accompanies the editorial reports that RAS mutations frequently occur in secondary skin tumors that develop in vemurafenib-treated patients.

The testing is necessary because there is "potential for secondary tumor development" that arises from treatment with vemurafenib and other BRAF inhibitors, writes Ashani T. Weeraratna, PhD, from the molecular and cellular oncogenesis program at The Wistar Institute in Philadelphia, Pennsylvania, in her editorial.

These secondary skin tumors — namely, cutaneous squamous cell carcinomas and keratoacanthomas — are relatively benign, compared with melanoma, and are no reason to discontinue vemurafenib, said Dr. Weeraratna. However, testing will alert clinicians to which patients have RAS-driven secondary tumors.

The testing is important because patients with RAS mutations could also develop secondary cancers in organs beyond the skin, advised Dr. Weeraratna.

"If patients have RAS mutations they should be monitored closely for any development of cutaneous squamous cell carcinomas in all organs," she told Medscape Medical News.

"Although cutaneous squamous cell carcinomas are not deadly, these lesions can be life-threatening when they occur in other organs," Dr. Weeraratna writes in her editorial.

She discussed other potentially affected organs.

"Squamous cell carcinomas can potentially arise in any organ with a squamous epithelium, essentially a layer of flattened epithelial cells that line the basement membranes of organs. A squamous epithelium is found most often in organs where rapid filtration and diffusion is necessary, such as the alveolar lining of the lungs and the glomerulus (kidney). Thus, squamous cell carcinomas can be found in organs such as the lungs, cervix, and esophagus, and also account for a large proportion of head and neck cancers," Dr. Weeraratna explained.

Importantly, there is no evidence that vemurafenib triggers tumors in other organs. "It is as yet unclear whether the generation of squamous cell carcinomas in these organs, upon BRAF inhibitor therapy, occurs, but these data certainly alert us to that potential risk," she said.

MEK Inhibitors May Help

In this study of melanoma patients, the investigators sought to characterize the molecular mechanism behind the development of secondary skin cancers in patients treated with vemurafenib.

They admit that a skin cancer drug that causes other skin cancers is unexpected.

The development of cutaneous squamous cell carcinomas and keratoacanthomas "is the opposite of what would be expected from a targeted oncogene inhibitor," write the study authors, led by Fei Su, PhD, from Hoffman-La Roche Pharmaceuticals in Nutley, New Jersey.

In their search to understand this toxicity, the investigators analyzed the DNA of a sampling of these tumors and found a high rate of RAS mutations (21 of 35 tumors; 60%).

"Mutations in RAS, particularly HRAS, are frequent in cutaneous squamous cell carcinomas and keratoacanthomas that develop in patients treated with vemurafenib," write the authors.

"This study points out that BRAF inhibitors should only be used in patients who have cancers driven by BRAF mutations, and it raises the concern that cancers driven by RAS mutations (KRAS, HRAS, or NRAS) can be paradoxically activated instead of inhibited with this class of drugs," said coauthor Antoni Ribas, MD, PhD, in email correspondence with Medscape Medical News. He is from the division of hematology–oncology at the UCLA Medical Center in Los Angeles, California.

Why patients treated with vemurafenib have such a high rate of RAS mutations in these secondary cancers is not known.

However, the investigators performed animal-model studies that suggest that the development of RAS-mutation-driven secondary tumors might be prevented with a MEK inhibitor, another class of drugs. There might be "usefulness of combining a BRAF inhibitor with a MEK inhibitor to prevent this toxic effect" of secondary cancers, write the authors.

There has already been clinical investigation of this concept — a phase 2 study of the combination of the MEK inhibitor GSK1120212 and the RAF inhibitor GSK2118436 in metastatic melanoma.

That study, which was presented at the 2011 annual meeting of the American Society of Clinical Oncology, and reported at that time by Medscape Medical News, showed that the toxicity of the combination seemed to be lower than that of either agent used alone.

N Engl J Med. 2012;366: 207-215, 271-273. Abstract, Editorial

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