Bortezomib Consolidation Following Upfront ASCT for Multiple Myeloma Deepens Disease Response and MRD-Negative Rate without Compromising Response to Subsequent Bortezomib Salvage: Results of a Phase II Study

Background: Consolidation after high dose therapy and autologous stem cell transplant (ASCT) for multiple myeloma (MM) can improve response depth and prolong progression free survival (PFS), but it is important to ensure good quality of life (QoL) and responsiveness to further salvage therapy. We conducted a single-arm Phase II weekly bortezomib consolidation trial (BCT) to assess outcomes in MM patients receiving upfront ASCT.

Methods: Bortezomib-na•ve patients with at least stable disease at 3-4 months post-high dose melphalan 200mg/m² with ASCT received up to 8 cycles of bortezomib (1.3mg/m² days 1,8,15,22 in a 4-week cycle), 17 intravenously (IV) and 23 subcutaneously (SC). The primary endpoint was disease response (IMWG) at 6 and 12 months post-ASCT. Other endpoints were MRD by multiparametric flow cytometry (patient 15 onwards) at 6 and 12 months post-ASCT, toxicity, PFS, overall survival, osteoblast function and Qol (EORT-QLQ-C30). Serum basic alkaline phosphatase (bALP) and ostocalcin (OC) were measured by ELISA.

Results: The study recruited 40 patients between December 2009 and March 2014 at a median of 3.4 months post-ASCT. The median age was 61 years (range 43-69); 55% male; isotypes were: 22 (59%) IgG, 9 (24%) IgA, 1 (3%) IgD, 5 (14%) light chain only, 1 non-secretory and 2 unknown. Induction regimens pre-ASCT were thalidomide (33, 87%), idarubicin and dexamethasone (5, 13%). and unknown in 2.

One patient was withdrawn prior to commencement (unfit for treatment) and 3 patients stopped trial treatment after 1 cycle (2 toxicity, 1 disease progression). Of 36 patients who completed >1 cycle of bortezomib, 10 stopped treatment early (5 toxicity, 4 patient choice, 1 disease progression); median number of cycles received was 8. Eleven (28%) patients experienced a total of 15 grade 3 adverse events (AE); 6 (neuropathy, 3 in IV group, 18% cf 3 in SC group, 13%), 4 (infection), 1 (fatigue), 2 (haematological), 2 other. One patient had a grade 4 infection (cycle 1, treatment discontinued) and 1 grade 4 back pain. EORTC-QLQ-C30 scores for global health status and physical, emotional and social functioning did not change significantly throughout treatment.

After a median follow up of 44.4 months, 18 (45%) are alive without progression, 20 (50%) are alive with progression and 2 (5%) died after progression. BCT improved response depth in assessable patients who completed >1 cycle (n=34). Disease response at trial entry: 4 (12%) sCR/CR, 19 (56%) VGPR, 10 (29%) PR, 1(3%) SD, cf. response at 12 months post-ASCT: 7 (21%) sCR/CR, 22 (65%) VGPR, 4 (12%) PR, 1(3%) PD. Biochemical response depth improved in 12 patients. 19 patients had MRD testing at 3 (where available) or 6 months post-ASCT and again at 12 months, 10 were MRD+ at the earlier time point, of whom 4 converted to MRD- at 12 months. Of the 9 MRD- patients, all remained negative at 12 months. 15 patients (44%) had improvement in biochemical and/or MRD response at 12 months.

Median PFS was 38.5 months (95%CI 29.1-47.9)(Figure). Patients who were MRD- at 12 months had median PFS of 49.2 months (95%CI 35.3-63.2) compared with 22.0 months (95%CI 21.5-22.6) in MRD+ patients (p=0.03).

Of the 22 patients who relapsed, 12 received bortezomib-based salvage regimens, 5 received carfilzomib-based regimens and 5 have not started second-line therapy. Disease responses in patients receiving bortezomib salvage was 8 (67%) VGPR, 4 (33%) PR. Four patients went on to have a 2^nd ASCT. In the 17 patients receiving salvage, median 2^nd PFS from start of second line was 14.8 months (95%CI 8.2-18.0).

At 3 months post-ASCT, levels of the osteoblast markers bALP and OC were significantly higher in CR/VGPR patients, compared to patients with PR or less (p=0.04 and 0.03, respectively). Neither marker changed significantly following BCT.

Conclusions: For patients with MM, consolidation with weekly bortezomib post-ASCT is well tolerated and deepens disease response and MRD negativity without compromising the response to subsequent bortezomib-based salvage therapy. Patients who are MRD- at 12 months enjoy a median PFS of 4 years. This low intensity post-ASCT strategy deserves further study in the context of current and evolving protocols for newly diagnosed patients.

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