Cobimetinib: inhibiting MEK1/2 in BRAF V600-mutant melanoma.

Historically, metastatic melanoma has had extremely poor survival outcomes. The outlook, however, is rapidly changing as new molecularly targeted therapies have vastly improved patient outcomes. One such therapy is the potent mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor cobimetinib. Recently, cobimetinib was approved for the treatment of metastatic or unresectable melanoma with serine/threonine-protein kinase B-raf (BRAF) V600E or V600K mutations when used in combination with the BRAF inhibitor vemurafenib. Currently, multiple clinical trials are investigating this drug combination for the treatment of various cancer types (e.g., breast, melanoma, colorectal). In the phase III coBRIM trial, this combination therapy showed improved melanoma response rates and patient progression-free survival when compared to vemurafenib alone. Additionally, toxicities were generally found to be manageable with dose modification or interruption. However, tumor response to BRAF/MEK inhibition, though rapid, is often short-lived as tumors develop resistance to this combination therapy. Therefore, new trials are beginning to investigate the addition of a third targeted agent or immunotherapy in order to increase the durability of treatment response. These trials are already showing promising preliminary results.