Clinical Efficacy of Daratumumab Monotherapy in Patients with Heavily Pretreated Relapsed or Refractory Multiple Myeloma

Abstract Introduction : Daratumumab (DARA) is a novel human CD-38-targeting monoclonal antibody in clinical development for multiple myeloma (MM). In two clinical studies (NCT00574288 [GEN501] and NCT01985126 [Sirius]), DARA monotherapy showed remarkable clinical activity and was well tolerated in heavily treated patients (pts) with relapsed and refractory (RR) MM (Lokhorst HM. J Clin Oncol 2014;32 Suppl:abstr 8513. Lonial S. J Clin Oncol 2015;33 Suppl: abstr LBA8512). A combined analysis of efficacy of 16 mg/kg DARA in these two studies is presented. Methods : GEN501, a first-in-human open-label, two-part (Part 1 dose escalation; Part 2 dose expansion) study, enrolled pts with MM that had relapsed after or were refractory to ≥2 prior therapies. Sirius, an open-label, two-part study, enrolled pts with MM with ≥3 prior therapies, including a PI or IMiD, or were refractory to both a PI and an IMiD. Eligibility criteria included pts with absolute neutrophil count ≥1000/mm3, hemoglobin ≥7.5 g/dL, platelet count ≥75×109/L (GEN501) or ≥50×109/L (Sirius), and alanine aminotransferase ≤3.5 (GEN501) or ≤2.5 (Sirius) times the upper limit of normal. In GEN501 Part 2, the first 16 mg/kg DARA infusion was followed by a 3 week rest period, and then qw for 7 weeks, q2w for 14 weeks, and q4w thereafter. In Sirius, 16 mg/kg DARA was infused qw for 8 weeks, q2w for 16 weeks, and q4w thereafter. The combined analysis comprised pts treated with 16 mg/kg DARA in Sirius and Part 2 of GEN501. In both studies overall response rates (ORR) were assessed according to IMWG response criteria. Results: The combined analysis included 148 pts (42 and 106 pts from GEN501 and Sirius, respectively). The median (range) age was 64 (31-84) years. Median time since initial diagnosis was 5.8 and 4.8 years in GEN501 and Sirius, respectively, and 62% and 82% of pts had received >3 prior therapies, respectively. In GEN501, 76% of pts were refractory to their last therapy and 64% were refractory to both a PI and IMiD; a greater proportion of pts in Sirius were refractory to their last therapy (97%) and double refractory to a PI and IMiD (95%). The ORR was 36% in GEN501 and 29% in Sirius; the ORR for the combined analysis was 31%. Best overall response is shown in Table. Responses deepened over time and the combined rate of very good partial response (VGPR) or better was 11% with 2 pts with complete responses (CR) and 3 with stringent CRs (sCR) across the two studies. In the combined analysis, median duration of response was 7.6 months and 46% of responders remained progression free at 1-year after a median follow-up of 9.3 months. Median overall survival (OS) had not been reached at median follow-up times of 10.2 months (GEN501) and 9.3 months (Sirius). The estimated 1-year OS rate (95% CI) was 77% (58-88), 65% (51-76), and 69% (58-77) for GEN501, Sirius, and the combined analysis, respectively. Forty-four of 46 responders were still alive at the time of the primary analysis. At a subsequent data cutoff for the combined analysis, after a median follow-up of 14.8 months, the estimated median OS was 19.9 months (95% CI, 15.1 - not estimable). ORR was similar across prespecified subgroups which included age, ISS stage, number of prior therapies, and refractory status. Conclusions : Single-agent DARA (16 mg/kg) demonstrated remarkable clinical activity (31% ORR) in a combined analysis of two studies in heavily pretreated MM pts. The quality of the observed responses (11% VGPR or better, 2 CRs, and 3 sCRs) was noteworthy in this highly refractory population. DARA shows promising activity in pts who have exhausted other approved myeloma treatment options. Table. Best Overall Response. 16 mg/kg MMY2002 n (%) GEN501 Part 2 n (%) Total n (%) Combined analysis set 106 42 148 Best response Stringent Complete Response (sCR) 3 (2.8) 0 3 (2.0) Complete response (CR) 0 2 (4.8) 2 (1.4) Very good partial response (VGPR) 10 (9.4) 2 (4.8) 12 (8.1) Partial response (PR) 18 (17.0) 11 (26.2) 29 (19.6) Minimal response (MR) 5 (4.7) 4 (9.5) 9 (6.1) Stable disease (SD) 46 (43.3) 22 (52.4) 68 (45.9) Progressive disease (PD) 18 (17.0) 0 18 (12.2) Not evaluable (NE) 6 (5.7) 1 (2.4) 7 (4.7) Overall response (sCR+CR+VGPR+PR) 31 (29.2) 15 (35.7) 46 (31.1) Disclosures Usmani: Celgene Corporation: Consultancy, Honoraria; Janssen: Research Funding; Onyx: Consultancy, Honoraria, Research Funding. Weiss:Janssen and Millennium: Consultancy; Janssen and Onclave: Research Funding. Bahlis:Johnson & Johnson: Research Funding; Amgen: Consultancy; Johnson & Johnson: Consultancy; Johnson & Johnson: Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau. Lonial:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Millennium: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Onyx: Consultancy, Research Funding. Lokhorst:Genmab: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Amgen: Honoraria. Voorhees:Janssen, Celgene, GlaxoSmithKline,Onyx Pharmaceuticals and Oncopeptides: Consultancy, Research Funding; Array BioPharma, Celgene, GlaxoSmithKline, and Oncopeptides: Consultancy; Millennium/Takeda and Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Richardson:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Millennium Takeda: Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees. Axel:Janssen: Employment. Feng:Janssen: Employment. Uhlar:Janssen: Employment. Wang:Janssen: Employment. Khan:Janssen: Employment. Ahmadi:Janssen: Employment. Nahi:Janssen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

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