Efficacy and Safety of Retreatment with Bortezomib in Patients with Multiple Myeloma: Interim Results From RETRIEVE, a Prospective International Phase 2 Study.

Abstract 3866

Poster Board III-802

Bortezomib (Velcade^®) retreatment has been shown to be active and well tolerated in patients with relapsed multiple myeloma (MM) in a number of retrospective studies and a small prospective phase 4 study (EVEREST). This large, prospective, international, multi-center, open-label phase 2 study was conducted to confirm the efficacy and safety of retreatment with bortezomib in MM patients who had previously responded (at least partial response [PR]) to bortezomib-based therapy as their most recent prior treatment. Patients had to have previously tolerated bortezomib 1.0 or 1.3 mg/m² alone or in combination and have had a treatment-free interval (TFI; time from last dose of initial bortezomib treatment to first dose of bortezomib retreatment) of ≥6 months. Additional eligibility criteria included progressive disease or relapse from complete response (CR) by EBMT criteria, no MM therapy (except maintenance with dexamethasone, thalidomide, or interferon) since the last dose of initial bortezomib treatment, KPS ≥60, and adequate renal, hepatic, and hematologic function; patients with grade ≥2 peripheral neuropathy or neuropathic pain (as defined by NCI CTCAE v3.0) were excluded. Patients received bortezomib at the last tolerated dose (1.0 or 1.3 mg/m²) during initial treatment on days 1, 4, 8, and 11 for up to eight 21-day cycles, either alone or in combination with dexamethasone at the investigator's discretion. Response was assessed by EBMT criteria every 6 weeks during treatment and then every 2 months until disease progression. Adverse events (AEs) were graded according to NCI CTCAE v3.0. A total of 130 patients received at least 1 dose of bortezomib retreatment and were included in the safety population. Patients had a median age of 67 years, 57% were male, and 16% had KPS '70%. Median time from diagnosis of MM was 4.5 years (range 0–14 years); median number of prior therapies was 2; 15, 80, 23, and 12 patients had received 1, 2, 3, and ≥4 prior lines of therapy (excluding initial bortezomib therapy). Best response by EBMT criteria to initial bortezomib treatment was CR in 26% and PR in 74% of patients; median time to progression and TFI after initial bortezomib treatment were 17.9 months and 14.3 months, respectively. Last tolerated dose of previous bortezomib therapy was 1.3 mg/m² and 1.0 mg/m² for 62% and 29% of patients, respectively; 9% received another dose. Patients received a median 7.0 (range 1–8) cycles of bortezomib retreatment (23% of patients completed all 8 cycles); 72% of patients received concomitant dexamethasone. A total of 126 patients were evaluable for response. In the 126 response-evaluable patients, the overall response rate (ORR; CR+PR) by best confirmed response (EBMT criteria) was 40%; in addition, 18% of patients achieved minimal response (MR), to give a CR+PR+MR rate of 58%. After a planned secondary efficacy analysis, the ORR (CR+PR) by single best response was 55% (75% ≥MR). Median time to best confirmed response (≥MR) was 2.9 months; time to first response was 1.5 months. Analysis of ORR by patient subgroups showed comparable results in patients who did versus did not receive concomitant dexamethasone (42% vs 32%), in those who received ≤1.0 mg/m² vs 1.3 mg/m² bortezomib (35% vs 41%), and in those aged ≤65 years vs >65 years (45% vs 36%). ORR was 67%, 39%, 33%, and 25% in patients who had received 1, 2, 3, and ≥4 prior lines of therapy (excluding initial bortezomib), respectively. Analysis of best confirmed responses according to response to initial bortezomib showed that 63% and 52% of patients who achieved a CR or PR, respectively, to initial bortezomib treatment responded to retreatment. Most (98%) patients experienced a treatment-emergent AE; 60% experienced a grade 3/4 AE, and 32% experienced a serious AE; there were 8 deaths, 2 of which (due to sepsis and stroke) were possibly treatment-related. The most common grade 3/4 AEs were thrombocytopenia (35%), neutropenia (7%), diarrhea (7%), and pneumonia (5%). AEs leading to dose reductions or discontinuations were reported for 22% and 12% of patients, respectively. The incidence of neuropathy was 39%, including 9% grade 3; 4% of patients discontinued treatment due to PN; 61% of neuropathy events resolved or improved within a median 1.3 months. These results confirm that bortezomib retreatment is a well-tolerated, feasible, and active therapeutic option for heavily pretreated MM patients without evidence of cumulative toxicity.