Pomalidomide, Dexamethasone and Pegylated Liposomal Doxorubicin For Patients With Relapsed/Refractory Multiple Myeloma: Results From a Phase 1/2 Trial

Background Thalidomide and its immunomodulatory drug (IMiD) derivatives such as lenalidomide (LEN) have shown great promise as treatment options for multiple myeloma (MM) patients (pts). Pomalidomide (POM) is a newer IMiD with high in vitro anti-MM potency that has shown promise as an effective treatment option for relapsed/refractory (R/R) MM pts. Recent data has shown POM to be effective in combination with dexamethasone (DEX), even for patients who are refractory to bortezomib and lenalidomide (Richardson et al, 2012). It has been demonstrated that the addition of pegylated liposomal doxorubicin (PLD) to lenalidomide and thalidomide is effective for both R/R and frontline MM pts (Offidani et al, 2006; 2007). Our recent trial evaluating lenalidomide in combination with dexamethasone, PLD, and bortezomib (DVD-R) showed that both efficacy and tolerability may be improved by changing the doses and schedules of these drugs (Berenson et al, 2012). These results imply that the combination of POM, DEX and PLD may be an effective regimen for treating R/R MM pts. We conducted a phase 1/2 trial investigating the safety and efficacy of POM in combination with IV DEX and PLD using our modified dose, schedule, and longer 28-day cycle for pts with R/R MM. Methods For enrollment into the phase 1 portion of the study, eligible pts had to show progressive MM at the time of enrollment. For participation in the phase 2 portion, pts had to be refractory to LEN (singe-agent or in combination) demonstrated by progressive disease while receiving this IMiD or relapsed within 8 weeks of their last dose. Pts who received previous POM treatment were ineligible. During the phase 1 part of the trial, POM was administered orally at 2, 3, or 4 mg daily in 3 successive cohorts of 3 pts each on days 1-21 of each 28-day cycle. DEX (40 mg intravenously over 30 min) and PLD (5 mg/m2infused over 30-90 min) both were given on days 1, 4, 8, and 11 of each cycle. POM doses were escalated per cohort until maximum tolerated dose (MTD) was reached. Phase 2 patients were all enrolled at what was established as the MTD. Results As of July 9, 2013, 33 pts were registered: 11 and 22 enrolled in the phase 1 and 2 portions, respectively. Fifteen patients have discontinued treatment thus far and 18 remain active. Pts had received a median of 5 prior treatments (range, 1-18) with a median of 1 prior PLD regimen (range, 0-2) and 1 prior IMiD regimen (range, 0-4). Pts have completed a median of 4 cycles (range: 0-8) with a median of 3.2 months of follow up (range: 0-9.7). During the phase 1 portion, no dose-limiting toxicities were identified, so the highest administered dose of 4 mg was initially established as the MTD. However, neutropenia ≥ G3 was observed in 10/17 phase 2 pts (58.8%) at this dose; and, as a result, the protocol was amended so that the MTD was lowered to 3 mg for all phase 2 pts beyond the 29thpt (n = 4). Thirty-two pts have received study drug. Twenty-nine pts were evaluable for response at data cutoff as 3 were active but had not yet had any post-baseline disease assessments. Of the 29 considered evaluable, overall response rate and clinical benefit rates were 34.5% and 48.3%, respectively, Six pts (20.7%) showed stable disease while 8 (27.6%) pts exhibited progressive disease. There was ≥ grade 3 (G3) neutropenia in 12 (37.5%) pts. Two pts experienced this toxicity during the phase 1 portion (3 mg and 4 mg doses- 1 each) whereas the other 10 pts experienced this side effect at the 4 mg dose during phase 2 enrollment. Following the lowering of the MTD to 3 mg due to this issue, neutropenia (≥ G3) has not been observed to date. Other treatment-emergent AEs ≥ G3 occurring in more than 1 pt were leukopenia in 12 (37.5%), lymphopenia in 8 (25%), anemia in 3 (9.4%), hyponatremia in 3 (9.4%), thrombocytopenia in 2 (6.3%), and duodenal ulcers in 1 (3.4%) pts. One pt died during treatment due to sepsis. Conclusions Results from this phase 1/2 trial demonstrate that the combination of pomalidomide with dexamethasone and PLD using a 28-day cycle shows efficacy for MM pts with progressive disease who are refractory to lenalidomide. Notably, less neutropenia has been observed at the 3 mg dose of pomalidomide, with 4 mg POM dosing associated with a high incidence of ≥ G3 neutropenia when used in this three-drug combination. Disclosures: Berenson: Celgene: Honoraria, Research Funding, Speakers Bureau. Swift:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Vescio:Celgene: Speakers Bureau.