A Phase 1/2 Multi-Center, Randomized, Open Label Dose Escalation Study to Determine the Maximum Tolerated Dose, Safety, and Efficacy of Pomalidomide Alone or in Combination with Low-Dose Dexamethasone in Patients with Relapsed and Refractory Multiple Myeloma Who Have Received Prior Treatment That Includes Lenalidomide and Bortezomib.
Authors: Richardson Paul , Siegel David , Baz Rachid , Kelley Susan L. , Munshi Nikhil C. , Sullivan Daniel , McBride Laura , Doss Deborah , Larkins Gail , Jacques Christian , Donaldson Arlene , Anderson Kenneth C. 
Published: October 2019

Abstract
Abstract 301

Background:
Pomalidomide (POM) is an IMiD® derived from thalidomide with a modified chemical structure with improved potency in vitro and potential efficacy and safety benefits in vivo. Two phase (Ph) 1b, single-center, ascending dose, open-label studies in pts with relapsed/refractory multiple myeloma (MM; Schey et al, 2004, Streetly et al, 2008) identified maximum tolerated dose (MTD) as 2mg QD or 5mg on alternate days (28 of each 28-day cycle). High response rates of POM alone in heavily pretreated pts were encouraging. To evaluate the MTD, safety and efficacy of POM alone or with Dexamathasone (dex) on a 21/28 day schedule, a Ph 1/2, multicenter, randomized, open-label, 3×3 dose-escalation study was initiated in pts with relapsed/refractory MM after at least 2 prior regimens, including bortezomib and lenalidomide.

Methods:
The study has a Ph 1 POM MTD (n=32) portion, followed by Ph 2 open-label randomized POM+ dex vs POM alone (192 pts planned). Eligible pts had documented relapsed/refractory MM. All pts received low-dose prophylactic aspirin QD and monitored for venous thromboembolic events (VTE). In Ph 1, POM was given QD on Days 1–21 of 28-day cycle: 4 dose levels of POM (2, 3, 4, 5mg) were studied with option to add dex at 40 mg/wk after 4 cycles for lack of response or progressive disease (PD). Pts enrolled in Ph 1 and discontinued either for intolerance or PD could not be enrolled in Ph 2. Toxicities and responses were assessed using CTCAE v3 and modified European Group for Blood and Marrow Transplantation (EBMT) criteria.

Results:
Results from Ph 1 of the study are reported with 32 pts enrolled to date. Fifteen pts discontinued therapy and 17 pts are ongoing for both safety and efficacy analyses. Mean age is 66.6 yrs (range 38–84), with median number of prior regimens 7 (range 2–18). MTD has not yet been reached. There were 4 dose reductions due to POM (5mg [2-neutropenia, 1-rash]; 3mg [1-neutropenia]) after 108 completed cycles. Neutropenia and thrombocytopenia were the most common grade 3/4 toxicities, with no dose-dependent increase apparent so far: 12 serious adverse events (SAEs) occurred in 10 pts; drug related events included POM (VTE, syncope, 3rd degree AV block, asthenia, diarrhea, neutropenia, anemia, rash); dex (lung infection with neutropenia); POM + dex (sepsis with pharyngeal abscess). AEs such as somnolence (1) VTE (1) neuropathy (2), and constipation (4) were uncommon. There were 3 deaths on study not attributed to POM; 2 pts died of rapid PD, 1 pt died of gastrointestinal perforation due to amyloidosis. Responses were seen at each dose level (Table 1). In 20/21 (95%) evaluable pts, clinical activity (SD or better) was reported. During treatment with POM alone, overall response rate (ORR; 1 CR, 2 PR, 5 MR) was 38% (8/21), mean duration of response (DOR) was 11.1 (range 4–32) wks, mean time to progression (TTP) was 8.3 (range 2–36) wks. Median completed cycles of POM +/− dex overall was 4 (range 1–12), with 13/21 evaluable pts (62%) having dex added to their regimens at various different cycles (median cycle 3, range 2–9) for PD or lack of response. During treatment with POM+dex, ORR (2 PR, 3 MR) was 38%, mean DOR of 14.2 (range 4–32) wks, and mean TTP of 20 (range 4–52) wks. In addition, there were 9 stable diseases (SD) on POM alone with mean DOR of 7.1 (range 4–16) wks, and 6 SD on POM + dex with mean DOR of 10.7 (range 8–16) wks. In 5/13 pts (38%), responses improved after dex was added (2 PR, 2 MR, 1 SD).

Conclusions:
These preliminary results indicate that POM alone or in combination with dex is associated with 38% MR or better, while SD was achieved in 43% (POM alone) and 46% (POM + dex), amongst heavily pretreated pts with relapsed/refractory MM. The incidence of SAEs and discontinuations decreased with increased dose of POM with no dose-dependent increase in grade 3/4 hematological toxicities. The MTD has not been reached to date. Overall, these data indicate that POM has an acceptable safety profile and is a clinically active therapeutic option for advanced refractory MM, warranting further investigation in this patient population.

Disclosures:
Richardson: Gentium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Keryx Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; Millenium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Johnson and Johnson: Membership on an entity's Board of Directors or advisory committees. Off Label Use: Pomalidomide is an anti-proliferative and immunomodulatory agent that is in clinical development for relapsed/refractory MM. Siegel:Celgene: Speakers Bureau; Millenium Pharmaceuticals: Speakers Bureau. Baz:Celgene: Research Funding. Munshi:Novartis Pharmaceuticals: Consultancy, Speakers Bureau; Millenium Pharmaceuticals: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau. Sullivan:Merck: Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees; Merrion: Membership on an entity's Board of Directors or advisory committees. Doss:Celgene: Speakers Bureau. Larkins:Celgene: Employment, Equity Ownership. Jacques:Celgene: Employment. Donaldson:Celgene: Employment. Anderson:Celgene: Consultancy, Honoraria, Speakers Bureau; Millenium Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau.