The Activity and Toxicity of Dasatinib in Relapsed or Plateau-Phase Multiple Myeloma.

Dasatinib (Sprycel®) is an orally administered inhibitor of multiple tyrosine kinases, which has been approved for the treatment of CML in chronic phase, accelerated phase or blast phase with resistance or intolerance to prior therapy including imatinib. In vitro studies have demonstrated that dasatinib inhibits the viability of multiple myeloma cell lines. Based on the in vitro activity of dasatinib against multiple myeloma, we initiated an open label, single-arm Phase II trial of dasatinib in relapsed, refractory or plateau-phase multiple myeloma; planned enrollment is 21 patients (pts). Treatment consists of dasatinib 70 mg p.o. twice daily continuously. The primary endpoint of the study is the overall response rate (CR+PR). Secondary endpoints include the time to response, duration of response, time to progression as well as tolerability and safety of dasatinib in this population. To date, 13 pts have been enrolled. The median age is 58 (range 38–76). Stage at diagnosis was: IIA (1 pt), IIIA (11), IIIB (1); 9 pts had IgG paraprotein and 4 had IgA. Median beta2-microglobulin at study entry was 3.2 (range 1.2–13). The median number of prior therapies was 2 (range 1–14); 12 pts had undergone prior autologous stem cell transplant. At enrollment, 7 pts had progressive disease and 6 pts had plateau phase disease, defined as at least 3 months with a stable paraprotein level (±25%) following the most recent therapy. At a median follow-up of 39 days (range 1–134 days), results are as follows: 4 patients have stable disease (SD); 7 patients had progressive disease (PD); 1 pt discontinued therapy due to toxicity (Grade II diarrhea, flushing and fatigue); 1 pt is not yet evaluable for response. Of those who remain on therapy, the median time on therapy is 39 days (range 1–134); 4 of these 5 patients had plateau phase disease at enrollment. Of those who discontinued therapy for PD, median time on therapy was 46 days (range 15–91); 6 of these 8 patients had PD at the time of enrollment. Toxicities have been manageable. Hematologic toxicities were more pronounced in the patients who had cytopenias at baseline. There was 1 episode of Grade III neutropenia, 4 episodes of Grade III anemia, 2 episodes of Grade III thrombocytopenia, and 3 episodes of Grade IV thrombocytopenia. Grade III non-hematologic toxicities have included: pneumonia (3 pts), acute renal failure (2), headache (1), epistaxis (2), febrile neutropenia (1), pulmonary edema (1), GI bleed (1), fatigue (2), hypertension (1), and hip pain (1). There was 1 episode of grade IV hypoglycemia. Enrollment and evaluation of responses/toxicities are ongoing. The protocol is being amended to allow for dose escalation to dasatinib 100 mg b.i.d. for stable disease at 8 weeks on therapy.