Don’t Use Vemurafenib in Earlier-Stage Melanomas

http://www.medscape.com/viewarticle/754542

December 1, 2011 — Vemurafenib (Zelboraf, Plexxikon/Roche) should not be used outside of its labeled indication for certain melanoma patients, a group of oncologists writes in an editorial published online November 7 in the Journal of Clinical Oncology.

They say that this new drug and other RAF inhibitors could theoretically cause second cancers over time.

http://www.medscape.com/viewarticle/754542

December 1, 2011 — Vemurafenib (Zelboraf, Plexxikon/Roche) should not be used outside of its labeled indication for certain melanoma patients, a group of oncologists writes in an editorial published online November 7 in the Journal of Clinical Oncology.

They say that this new drug and other RAF inhibitors could theoretically cause second cancers over time.

Vemurafenib was approved by the US Food and Drug Administration this year for the treatment of metastatic melanoma in patients with BRAF mutations, and has wowed the oncology community with its efficacy.

Consequently, clinicians could be tempted to try the drug in earlier-stage BRAF-mutant melanoma patients, especially those with high-risk surgically resected disease, suggest the editorialists, led by Mario Lacouture, MD, from the Memorial Sloan-Kettering Cancer Center in New York City.

But second cancers are a potential concern in earlier-stage melanoma patients, who will likely live longer than the typical patient with metastatic disease (9 to 12 months), they warn.

Interestingly, the second cancers of concern are not keratoacanthomas (KAs) or cutaneous squamous cell carcinomas (cSCCs), which have been cited as adverse events in clinical studies of vemurafenib. The editorialists are not especially worried about these 2 skin cancers, which develop in up to one third of all vemurafenib-treated patients. They explain: "The KAs and cSCCs that arise in the setting of vemurafenib treatment are of low metastatic potential, often regress spontaneously, and are easily cured by surgical resection and/or destructive methods (cryotherapy or electrodessication/curettage)."

Instead, there is a theoretical concern about tumors at other body sites.

"It remains unknown whether vemurafenib or other RAF inhibitors will promote the growth of dormant RAS mutant tumors of the lung, pancreas, or other sites," write Dr. Lacouture and his colleagues.

They explain that there is evidence to suggest that vemurafenib promotes the "hyperproliferation of preexistent dormant RAS mutant cancer cells."

How Lung, Pancreas, and Other Cancers Can Occur

To understand how selective RAF inhibitors such as vemurafenib can cause other tumors, one needs to look at an accompnaying genomic analysis of 237 cSCCs and KAs, 19 of which were from patients treated with RAF inhibitors (either vemurafenib or sorafenib), the editorialists explain.

The cSCCs and KAs from patients treated with RAF inhibitors have a mutational profile that is distinct from those that arose sporadically or as a result of treatment with immunosuppressive agents, say the editorialists. Specifically, 21.1% of KAs and cSCCs resected from patients treated with RAF inhibitors were found to have activating HRAS mutations, whereas RAS mutations were rare (3.2%) in tumors that developed in the other patients.

These study results, along with "the rapid appearance of cSCC and KA after initiation of vemurafenib," suggest that the "induction of RAF signaling" by vemurafenib promotes the growth of dormant RAS mutant cancer cells, the editorialists write.

There might be good news for melanoma researchers in this genomic analysis, say Dr. Lacouture and his colleagues. These results might "guide the development of combination strategies" in melanoma, which could result in the synergistic antitumor activity and attenuated toxicities that occur with either drug alone.

In support of this concept, they refer to a recent phase 2 study of the combination of the MEK inhibitor GSK1120212 and RAF inhibitor GSK2118436 in metastatic melanoma. The study, which was presented at the 2011 annual meeting of the American Society of Clinical Oncology, and covered 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.