Results of a Phase II Open-Label Trial of Bortezomib in Patients with Multiple Myeloma Who Have Undergone High-Dose Melphalan Therapy Followed by Autologous Peripheral Blood Stem Cell Transplantation and Failed to Achieve a Complete Response

Multiple myeloma (MM) is the second most common hematologic malignancy. Presently, the majority of suitable MM patients who undergo high-dose melphalan therapy followed by autologous peripheral blood stem cell transplantation (PBSCT) fail to achieve a complete response (CR). This suggests that treatment options following autologous transplantation are needed. Moreover, there is a need to determine the optimal role of maintenance therapy following PBSCT in MM. Over time, Bortezomib (B) has been shown to be an active agent in the treatment of newly diagnosed, and relapsed or refractory MM. Therefore, the primary objective of this study was to determine the efficacy of B treatment after high-dose melphalan therapy followed by PBSCT in MM. Fifty patients (pts) were enrolled between March 2004 and November 2007, and 47 were evaluable (2 pts ineligible and 1 pt data pending). Pts received B 1.3 mg/m² IV on Days 1, 4, 8, and 11 of each 21-day cycle. Pts were treated for 4 cycles or until evidence of disease progression or intolerable toxicity. If an improvement in response was noted after Cycle 4, pts could receive up to 4 additional cycles. To reduce the incidence of varicella zoster infection, antiviral prophylaxis (acyclovir 400 mg PO BID) was taken for the duration of the study. The median patient age was 56 years (range, 39–74), 82% were white, and 68% were male. The majority of pts (64%) had ECOG PS 0, 44% were Durie-Salmon Stage IIIA prior to induction therapy. Forty percent had symptomatic IgG-kappa multiple myeloma. Of all pts, 74% had a single transplant, while 24% had tandem transplants (2% [n=1 pt] data pending). Sixty-eight percent of pts had a PR and 18% had a MR following their transplant(s). While on study, pts received a median of 4 cycles (range, 2–8) of therapy with B. Efficacy results for the evaluable population are: CR 4%, unconfirmed (u) CR 4%, PR 21%, uPR 17%, MR 11%, and No Change 36%. Median time-to-treatment failure was 5.8 months (mos) (range, 0.2–19.4). There were 2 on-study deaths (sepsis and PD). Grade 3–4 treatment-related toxicities reported in >1 pt were thrombocytopenia (15%), asthenia (10%), neutropenia or neuropathy (8% each), peripheral neuritis (6%), and nausea (4%). Twenty patients discontinued study treatment due to toxicity (22%), pt request (6%), disease progression, ineligibility, and intercurrent illness/protocol deviation (4% each). 26 pts (52%) completed the study; 4 pts are still on study (8%). Sixteen pts started new treatment; median time from start of study treatment to the start of new treatment was 5.2 mos (range, 1.5–17.6 mos). The study was closed earlier than the planned due to the widespread availability of B, and the inability to find B-naïve patients. Bortezomib given after high-dose melphalan therapy and autologous PBSCT was well-tolerated with manageable adverse events. Updated cytogenetic analysis will be available for presentation.