Single agent bortezomib treatment yields ≥ partial responses (PR) in 24% of patients with relapsed, refractory multiple myeloma (MM) and 38% of patients who had received 1 – 3 previous therapies. Dexamethasone (DEX) adds to anti-myeloma activity of bortezomib. The present phase II trial was intitiated to study bortezomib combined with DEX and continuous low-dose oral cyclophosphamide (CY).

50 patients with advanced MM were scheduled to receive bortezomib 1.3 mg/m2 IV days 1, 4, 8, and 11 q 3 weeks for 8 cycles in combination with DEX 20 mg PO on the day of bortezomib injection and the day thereafter, and CY 50 mg PO daily; followed by 3 cycles bortezomib 1.3 mg/m2 IV days 1, 8, 15, and 22 q 5 weeks in combination with corresponding DEX and CY schedules. Patient characteristics included median age 63 years; B2M > 3,0 mg/L, 64%; CRP > 3,0 mg/L, 25%; deletion of chromosome 13, 46%; median number of prior regimens, 2 (range 1 – 9), and prior standard therapy > 12 mo, 94 %. 78% of patients had relapsed after high-dose melphalan. The EBMT criteria were used for definition of response. Five patients (10%) achieved a complete response, 33 (66%) a PR, and 6 (12%) a minor response (MR) resulting in an overall response rate (≥MR) of 88%. On an intention-to-treat basis, median event-free survival (EFS) with this combination was 10 months. After a median follow-up of 10 months, median overall survival has not been reached. Notably, chromosome 13 deletion was predictive of a favorable outcome (higher response rate, longer EFS) in this setting.

The median number or treatment cycles given was 6. 56% of the patients terminated study treatment prematurely, mainly for disease progression (10%) or adverse events (34%). Grade 4 neutropenia during at least one treatment cycle occurred in one patient (2%), grade 4 thrombocytopenia in 17%; one thrombocytopenic bleeding. Grade 3/4 non-hematologic toxicities requiring dose or schedule modifications included infections (26%), peripheral neuropathy (25%), fatigue (15%), herpes zoster (13%), and cardiovascular events (11%). One patient succumbed to infection without predisposing neutropenia.

Bortezomib in combination with DEX and CY appears to be a highly active regimen without increased toxicity compared to a single agent treatment with bortezomib. Maintenance treatment might be required for prolonged EFS.