Response to Proteosome Inhibitors and Immunomodulatory Drugs before and after Allogeneic Transplantation in Patients with Multiple Myeloma: A Long Term Follow up Study

Introduction: Allogeneic haematopoietic stem cell transplantation (alloHCT) is a potentially curative approach for patients (pts) with multiple myeloma (MM). The high transplant related mortality (TRM) rate with myeloablative conditioning has resulted in a shift to reduced intensity conditioning regimens (RIC). However, most MM pts who receive an alloRIC ultimately relapse and their treatment remains a challenge. Since alloHCT can modify the biology of the disease, including the immune environment, responses after alloHCT to rescue therapies previously used before alloHCT could be improved. Our main objective was to evaluate the efficacy of regimens including new drugs in MM pts relapsing after alloHCT comparing the efficacy achieved before and after alloHCT.

Material and Methods: We report a retrospective multicenter analysis of 126 consecutive pts that underwent alloHCT for MM from 2010 to 2013 at 8 Spanish centers.

Results: Baseline pts and transplant characteristics are shown in Table I. The median of prior therapies prior to alloHCT was 3 (1-9), 83% had received previous autologous HCT and 26% had high risk cytogenetic. 71 (56%) and 48 pts (38%) had been treated with regimens containing proteasome inhibitors (PI) and immunomodulatory drugs (IMIDs) before transplantation, respectively. Disease status at transplant was complete remission (CR) in 16 (13%) pts, partial response (PR) or very good PR in 86 (68%) and 24 (18.5%) had relapsed/progressive disease. 35 pts (28%) had active extramedullary disease at transplant. The majority of pts received peripheral blood HCT (90%), RIC (90%) with fludarabine plus melphalan based conditioning regimen (61%) and calcineurin inhibitor plus MTX as GVHD prophylaxis (68%). 19% receiving allo-HCT from an unrelated donor (91% 10/10 HLA matched).

All pts engrafted. Grade II-IV acute GVHD occurred in 54% pts (grade IV 8%) and chronic GVHD in 45% (moderate 15%, severe 12%). TRM within the first 100 days after transplant was 6% (overall TRM 28%). 60% pts improved their pre-transplant response, with an overall response rate of 74% (56% CR). After a median follow-up of 92 months for pts alive (22-197), the OS was 51 and 43% at 2 and 5 years respectively.

75 pts (59.5%) relapsed after alloHCT, 57 of them with extramedullary involvement. Median time to relapse was 8 months post-transplant (1-141). The cumulative incidence of relapse was 79% at 3 years. Median OS after relapse was 22 months (8-33).

Seventeen out of 75 pts who relapsed received IP both in the pre-transplant and in the post-transplant period. Sixteen pts out of 17 who received IP achieved at least PR pre-transplant while 10 out of these 16 pts responded again to PI post-HCT. Moreover, 1 patient reached a deeper response (CR) post as compared to pre alloHCT (PR) and 1 patient who was refractory pre-alloHCT did respond post-alloHCT. In addition, 6 out of 7 pts who did not respond to IP post-transplant reached stable disease with time to progression (TTP) lasting 4 to 12 months.

Twelve out of 75 pts who relapsed received IMIDs both pre and post-alloHCT. Ten pts out of 12 who received IMID pre-alloHCT achieved at least PR, and 8 out of these 10 pts responded again to IMIDs post-alloHCT. Moreover, 1 patient who had been refractory to IMIDs in the pre-transplant period reached CR after alloHCT. In addition, 2 out of 4 pts who were refractory to IMIDs in the post-transplant period reached stable disease with TTP of 8 to 13 months.

Remarkably, among pts who respond both in the pre and the post-transplant period to IP or IMIDs, the time to response (TTR) and time to progression (TTP) was similar despite the regimens used in the pre-transplant setting were more aggressive (TTR 3 vs 3.5 and TTP 9 vs 7 months before and after alloHCT for IP, and TTR 4 both before and after alloHCT and TTP 10 vs 9.5 months before and after alloHCT for IMIDs).

All but 2 pts received first generation IP pre and post-alloHCT (two pts received carfilzomib) and all but 5 received first generation IMIDs (5 pts were treated with pomalidomide).

Conclusions: MM pts relapsing after alloHCT should be considered candidates to receive new drugs, as they can achieve response rates at least in a similar proportion and durability to those observed in the pre-transplant setting. This finding is in contrast to the usual course of the disease outside the alloHCT setting, where response rates and TTP decreases with consecutive lines of treatment.