A retrospective analysis of bortezomib therapy for Japanese patients with relapsed or refractory multiple myeloma: β2-microglobulin associated with time to progression

Bortezomib is approved for the treatment of patients with relapsed or refractory multiple myeloma (MM), but only a few clinical studies for Japanese patients who were treated with bortezomib have been reported. We retrospectively analyzed 40 patients with relapsed or refractory MM who have received bortezomib at three collaborating centers in Miyagi prefecture in Japan. All the patients have been received bortezomib in combination with dexamethasone. Responses were determined using International Myeloma Working Group uniform response criteria. The overall response was observed in 30 patients (75%), including very good partial response in 8 patients (20%), and partial response in 22 patients (55%). The median time to disease progression was 8.7 months, and the median overall survival has not been reached. The factors affecting time to disease progression were International Staging System stage, serum β2-microglobulin level, and number of treatment cycles. The most common grade 3 and 4 adverse events were thrombocytopenia (50%), peripheral neuropathy (25%), leukopenia (25%), and herpes zoster infection (25%). Thus, bortezomib is well tolerated and effective for Japanese patients with relapsed or refractory MM. Our results suggest that serum β2-microglobulin level may be a marker of prognosis on bortezomib therapy for patients with relapsed or refractory MM although further studies are needed.