A Phase II Study of PS-341 for Patients with High Risk, Newly Diagnosed Multiple Myeloma: A Trial of the Eastern Cooperative Oncology Group (E2A02).

Background: Multiple myeloma (MM) is an incurable disease with a anticipated overall survival (OS) ranging from months to decades. Modest improvements in OS have been made with high-dose chemotherapy with peripheral blood stem cell transplant (PBSCT), but to date prognostic factors have a greater impact on OS than do individual therapies. Patients with adverse risk factors such as elevated beta-2 microglobulin (B2M), plasma cell labeling index, deletions of the long arm of chromosome 13 by metaphase cytogenetics (del 13q) require innovative new treatment strategies. Bortezomib has significant activity in patients with both newly diagnosed and relapsed/refractory MM, but its specific role in patients with adverse features has not yet been defined.

Methods: Patients with newly diagnosed “high-risk” myeloma (B2M ≥ 5.5., PCLI ≥ 1, or del 13q) and adequate organ and functional status were eligible. Patients were treated with bortezomib 1.3 mg/m2 day 1, 4, 8, and 11 every 21 days for 8 cycles as induction. After induction, patients were scheduled to receive bortezomib 1.3 mg/m2 every other week indefinitely. Elective peripheral stem cell mobilization (growth factor alone) was allowed after 4 cycles of bortezomib. Patients relapsing on maintenance schedule were to have the full induction schedule resumed. Responses were by the EBMT criteria but a very good partial response category was included. The primary end-point was the response rate in these high-risk patients (90% power to detect a response rate of 50% or higher). The study decision rule requires that 16 or more responses, among 39 eligible patients, are seen in order to declare this treatment effective.

Results: Between March 15, 2004 and March 10, 2005, 44 patients enrolled on study. Among the 43 eligible patients, median age was 63; 51% were male. All patients had high risk disease: del 13q (6/41); plasma cell labeling index ≥1% (16/34); and B2M≥5.5 (34/43). Preliminary response data are available for 18 of the 44 cases enrolled, of which 7 had partial response, 1 had minimal response, 1 had no response, 2 had progressive disease, and 5 were unevaluable. Among those patients completing induction therapy and with response information, the median number of cycles of therapy administered is 5, range (0,8). The most common non-hematologic adverse events (AEs) of grade 3 or higher included hyponatremia (9 patients) and diarrhea (6 patients). Mild sensory peripheral neuropathy was common: grade 1, 16 patients; grade 2, 2 patients. Only 1 patient had grade 3 peripheral neuropathy. One patient died after receiving 2 doses bortezomib due to heart block and asystole. Two patients had a grade 4, 25 patients had grade 3, and 13 had grade 1 or 2 as the worst grade non-hematologic adverse event. Based on data received by August 1, 2005, 18 patients have gone off study: AEs (2); death (1); progressive disease (9); and other reasons (6). Updated results on the full study population along with FISH data for IgH translocations and deletions of 13q and 17p will be presented at the meeting.

Conclusions: Preliminary results suggest that upfront bortezomib has activity in patients with high-risk MM, but further follow-up is required.