Real-World Use of Pomalidomide and Dexamethasone in Double Refractory Multiple Myeloma: A Multicentre UK Experience
Authors: Maciocia Nicola , Melville Andrew , Maciocia Paul Michael , Cheesman Simon , Sharpley Faye , Ramasamy Karthik , Streetly Matthew , Jenner Matthew W , Benjamin Reuben , Schey Stephen A , Popat Rakesh , D'Sa Shirley , Rismani Ali , Yong Kwee L , Rabin Neil 
Published: October 2019

Abstract
Introduction. The outlook for myeloma patients who relapse after or become refractory to bortezomib and IMiDs is poor, with limited therapeutic options and a median survival (OS) of 9 months. In the phase 3 MM-003 study, pomalidomide plus low-dose dexamethasone resulted in a significant PFS (median 4 vs 1.9 months) and OS (median 13.1 vs 8.1 months) benefit, compared to high-dose dexamethasone. Information on real-world outcomes of pomalidomide therapy is limited. We carried out a retrospective analysis of patients receiving pomalidomide in the UK, to compare outcomes and tolerability with published clinical trial data, and focus on high risk subgroups.
Methods. All patients treated with pomalidomide at 5 major UK centres between August 2013 and March 2016 were identified from chemotherapy records, and clinical data including toxicity and survival from patient records. Disease response and adverse FISH were defined as per IMWG. Survival was estimated using Kaplan-Meier, and correlations made using log-rank methods. Key subgroups: eGFR <45ml/min, adverse genetics, and older age were assessed.
Results. A total of 85 patients were identified. Of these, 70 (82%) had measurable disease (IMWG criteria) and received ≥1 cycle so were included in response analyses. Baseline patient characteristics are reported in Table 1.
96.5% of patients were refractory to one or more IMiDs, and 72.9% were refractory to both IMiDs and bortezomib. 92.9% were refractory to their last treatment. The median dose of pomalidomide was 4mg (2-4). Grade 3-4 non-haematological toxicities occurred in 42.4%: pneumonia (16.5%), neutropenic sepsis (8.2%), and acute kidney injury (7.1%), were most common. Grade 3-4 neutropenia occurred in 38% and thrombocytopenia in 24%. Seven patients died on treatment, 6 during the first cycle (2 PD and sepsis, 2 neutropenic sepsis, 1 PD and AKI, 2 pneumonia).
In the 70 patients assessable for response, ORR was 52.9% (5.7% VGPR, 47.1% PR, 38.6% SD). Median duration of response (DoR) was 4 months. With median follow-up of 13 months, median PFS was 5 months (95%CI 3.6-6.4), and median OS 13 months (95%CI 10.8-15.2).
Patients with renal failure (eGFR <45ml/min) had PFS and OS that were similar to those with eGFR ≥45ml/min ((HR=0.95, 95%CI 0.49-1.82, and HR=1.22, 0.59-2.53). Patients with adverse FISH (44%) had similar outcomes to those with standard FISH (ORR 45.8 vs 50%, median PFS 6 vs 5 months (HR=0.86, 95%CI 0.44-1.67, and median OS 10 vs 8 months, HR=1.223, 0.55-2.68). Patients aged >65yrs had similar outcomes to younger patients,(ORR 54.1 vs 51.5%, median PFS and OS comparable between groups). Rates of toxicity were also not influenced by renal impairment, adverse genetics, or older age.
The most important predictors of PFS and OS were depth and durability of response. PFS was 6 months for patients achieving PR, 4 months for SD and 1 month for PD, while OS was 18 months in patients achieving PR, 13 months for SD and 3 months for PD. For patients with DoR >4 months, PFS was 11 months and OS 23 months. In contrast, in patients whose DoR was < 4 months or who did not respond, OS was 9 months.
Conclusions. Our real-world data on the characteristics and outcomes of patients receiving pomalidomide for relapsed/refractory myeloma in the UK reflect results of published clinical trials. The ORR of 52.9% in our cohort is higher than in MM-003 and MM-010, but PFS (5 months) and OS (13 months) were remarkably similar. Rates of haematological toxicity and infections are low, confirming the good tolerability of pomalidomide in this patient group.
Depth and sustainability of response were important predictors of survival: achievement of PR was associated with improved PFS and OS, while patients who achieved SD still derived a survival benefit. Patients who maintained a response for at least 4 months had an estimated survival of nearly 2 years. No difference in response, survival or tolerability was seen in key subgroups, including those with moderate renal impairment, adverse cytogenetics and older age. Our findings confirm the efficacy of pomalidomide in these heavily pre-treated patients and add to the evidence for the benefit of pomalidomide in high risk patient groups.
Table Patient characteristics and comparison with MM003 trial Table. Patient characteristics and comparison with MM003 trial Figure 1 PFS and OS for the edited group of 70 patients Figure 1. PFS and OS for the edited group of 70 patients

Disclosures
Maciocia: Autolus: Equity Ownership, Patents & Royalties: TRBC1 and 2 Targeting for the Diagnosis and Treatment of T-cell Malignancies. Ramasamy:Celgene: Honoraria, Research Funding. Jenner:Novartis: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Other: Travel support; Amgen: Consultancy, Honoraria, Other: Travel support; Celgene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Other: Travel support, Research Funding. Schey:Celgene, Takeda: Honoraria; Celgene, Johnson & Johnson: Speakers Bureau; Celgene: Consultancy. Yong:Autolus Ltd: Equity Ownership, Patents & Royalties: APRIL based chimeric antigen receptor; Janssen: Research Funding.