A phase II trial of sorafenib in patients with relapsing and resistant multiple myeloma (MM) previously treated with bortezomib (S0434).

e19517 Background: The multikinase inhibitor sorafenib targets several serine/threonine and receptor tyrosine kinases by blocking RAF kinase, a critical component of the RAF/MEK/ERK signaling pathway regulated by the Ras oncogene, which is mutated both in primary patient samples and in human MM lines (35-50%). As the frequency of these mutations increases with advancing disease and increasing drug resistance, inhibition of the RAF/MEK/ERK signaling pathway, as well the angiogenic VEGFR-2/PDGFR beta cascade by sorafenib may be a useful new approach for the treatment of MM. METHODS SWOG evaluated the effect of sorafenib as a single agent in relapsed/refractory MM patients. In this phase II study we assessed response rate, overall (OS) and progression-free survival (PFS) as well as toxicities associated with this treatment. Twenty-three heavily pretreated MM patients were enrolled in the study. Sorafenib was started at oral dose of 400 mg daily until progression or toxicity. This dose was based on the label for metastatic renal cell carcinoma. RESULTS The study was closed as planned due to lack of efficacy in first 18 patients who were assessable for toxicity and response. Three patients experienced Grade 4 toxicity consisting of thrombocytopenia, anemia and renal failure. 8 cases suffered Grade 3 toxicities including thrombocytopenia, neutropenia, anemia, hand-foot syndrome, diarrhea and dyspnea. No responses were observed. 3 patients had stable disease (2.4-15.9 months) and the remainder progressed. Median PFS is one month, and OS at 12 months is 50%. CONCLUSIONS Thus, single agent sorafenib did not show activity in this group of heavily pretreated MM patients previously exposed to bortezomib. As the frequency of RAS oncogene mutations increases resulting in resistance to traditional chemotherapeutic agents as well as possibly supporting cytokine resistance to immune modulators, sorafenib might have a supportive role in combination therapy with bortezomib, lenalidomide or everolimus in relapsed/refractory MM which is currently being evaluated in ongoing studies. No significant financial relationships to disclose.