T(11;14) and High BCL2 Expression Are Predictive Biomarkers of Response to Venetoclax in Combination with Bortezomib and Dexamethasone in Patients with Relapsed/Refractory Multiple Myeloma: Biomarker Analyses from the Phase 3 Bellini Study

Background: Overexpression of the anti-apoptotic BCL-2 protein promotes multiple myeloma (MM) cell survival. Venetoclax (Ven) is a highly selective, potent, oral BCL-2 inhibitor that induces apoptosis and has shown synergistic activity with bortezomib (B) and dexamethasone (d). Phase 1 studies in relapsed/refractory (RR) MM demonstrated encouraging clinical efficacy of Ven + d in t(11;14) MM and in a broader patient (pt) population in combination with Bd. Recent results from the Phase 3 BELLINI study of Ven vs placebo (Pbo) + Bd in pts with RRMM demonstrated that pts treated with Ven + Bd had improved clinical response rates and progression-free survival (PFS) vs Pbo, although the overall survival (OS) result was in favor of Pbo. Subgroup analyses showed different efficacy and survival outcomes based on tumor cytogenetics and BCL-2 expression. Results of pre-specified subgroup analyses and additional retrospective correlative biomarker analyses in the Phase 3 BELLINI study are described herein.Methods: BELLINI (NCT02755597) was a randomized, double-blind, multicenter Phase 3 study of Ven or Pbo + Bd in pts with RRMM who received 1-3 prior therapies and were either sensitive or naïve to PIs. Pts were randomized 2:1 to receive Ven 800 mg/day or Pbo + Bd. The following biomarker analyses were performed by central laboratory assessments of pre-treatment tumor samples: BCL-2 protein expression by immunohistochemistry (IHC) analysis of bone marrow (BM) core biopsies; BCL2 gene expression by quantitative PCR (qPCR) and cytogenetic abnormalities by interphase fluorescence in situ hybridization (FISH) analysis of CD138-enriched BM mononuclear cells. Correlation between BCL-2 (protein and gene) expression, cytogenetics, and outcomes were examined by Kruskal-Wallis tests and by hazard ratio (HR) using the Cox proportional hazard model.Results: As of the data cut-off of 18 Mar 2019, 291 pts were randomized, 194 to the Ven arm and 97 to the Pbo arm. Out of the 291 pts randomized, 177 pts (61%) were evaluable by IHC, 257 pts (88%) by qPCR, and 262 pts (90%) by FISH. A broad range of BCL2 gene expression was observed (median 2-DCt: 0.212 [range: 0-5.21]), which strongly correlated with protein expression (median 2-DCt 0.115 in BCL-2 IHC Low vs 0.277 in BCL-2 IHC High, p=0.0021). t(11;14) MM had the highest levels of BCL-2 expression (23/23 BCL-2 High by IHC; median 2-DCt 0.406 vs 0.212 in t(11;14) negative, p=0.0132), however high BCL-2 expression was not limited to the t(11;14) subgroup. Univariate analyses showed higher BCL2 expression in pt tumor samples with del(13q) (median 2-DCt 0.333 vs 0.159 in pts without del(13q), p=0.0008) and gain(1q) (median 2-DCt 0. 295 vs 0.180 in pts without gain(1q), p=0.0059). Bootstrapping and aggregating thresholds from trees (BATTing) was used retrospectively to identify an estimated threshold value for BCL2 expression (2-DCt ≥0.323) that could provide optimum selection of pts with maximum improvement in PFS when treated with Ven+Bd.Biomarker subgroups with the greatest PFS improvement were t(11;14) (HR=0.10; 95% CI: 0.02-0.46, p=0.003) and High BCL2 by qPCR (HR=0.26; 95% CI: 0.13-0.51, p<0.001; Table 1). Since the t(11;14) and High BCL2 patient populations do not completely overlap (20% of High BCL2 pts were t(11;14) and 54% of t(11;14) were High BCL2), a combined subgroup analysis was performed. For pts with t(11;14) or High BCL2, the median PFS was not reached in the Ven arm vs 9.9 mo in Pbo (HR=0.26, 95% CI: 0.14-0.48, p<0.001; Table 1). Higher overall response (ORR, 88% vs 70%), very good partial response or better (≥VGPR, 73% vs 33%), and complete response or better (≥CR, 42% vs 3%) rates were observed in the Ven vs Pbo arm (Table 2). Minimal residual disease negativity (MRD-, 10-5) rate was also higher for t(11;14) or High BCL2 pts in the Ven vs Pbo arm (19% vs 0%). Median overall survival (OS) was not reached in either arm but was similar between treatment arms for the combined group with t(11;14) or High BCL2 pts (HR=0.92, 95% CI=0.39-2.16, p=0.85). In contrast, in the t(11;14) negative and Low BCL2 pts, OS favored Pbo (HR=3.13, 95% CI=1.2-8.13, p=0.019; Table 1).Conclusions: Adding Ven to Bd demonstrates significant efficacy in pts with RRMM harboring either t(11;14) or tumor cells expressing high levels of BCL2. The benefit-risk profile appears to be favorable in these subsets of pts and additional studies to gain further safety and efficacy information are warranted.

Duke Scholars

Author Cristina Gasparetto Medicine, Hematologic Malignancies and Cellular Therapy