Real world outcomes of high dose melphalan conditioning prior to autologous stem cell transplant in extramedullary multiple myeloma vs. multiple myeloma without extramedullary involvement: A single center experience.

Abstract

7550 Background: Extramedullary multiple myeloma (EMM) is defined as the presence of multiple myeloma plasma cells, which develop outside of the bone marrow. It is an aggressive form of multiple myeloma that is associated with a poor prognosis. The current standard of care for multiple myeloma consists of induction, high dose melphalan autologous stem cell transplant (ASCT), followed by maintenance. However, there is limited data on the outcome of patients with extramedullary multiple myeloma who undergo ASCT. Therefore, we examined the outcomes of high dose melphalan conditioning prior to ASCT in EMM patients compared to multiple myeloma patients without extramedullary involvement (non-EMM) at an academic institution in Los Angeles. Methods: We retrospectively reviewed 246 multiple myeloma patients who underwent ASCT after receiving high dose melphalan conditioning at USC Norris Comprehensive Cancer Center from Jan 2017 to Dec 2022. The cohort was subdivided into 70 EMM patients and 176 non-EMM patients. Outcomes were measured as the status of disease response, which was evaluated at 100 days (D+100) and 365 days (D+365) after the date of transplant. Results: In the EMM group, 1.43% (n=1) was found to have progression at D+100 and 12.86% (n=9) at D+365. In the non-EMM group, 0.57% (n=1) was found to have progression at D+100 and 11.93% (n=21) at D+365. There was no statistical significance between the EMM and non-EMM groups for progression free survival at D+100 (p-0.50) and D+365 (p-0.75). Regarding overall survival, there were 0 deaths observed at D+100 in both the EMM and non-EMM groups. For D+365, the overall survival was 98.57% (n=69) for the EMM group and 99.43% (n=175) for the non-EMM group. There was no statistical significance between the overall survival at D+365 (p-0.14). Conclusions: The EMM cohort exhibited similar rates of progression free survival (87.14% vs. 88.07%) and overall survival (98.57% vs. 99.43%) compared to the non-EMM cohort at one year post ASCT after receiving high dose melphalan conditioning. We observed that there was no significant statistical difference between the EMM and non-EMM cohorts regarding progression-free survival (p-0.75) and overall survival (p-0.14) on day 365. According to our data, high dose melphalan conditioning prior to autologous stem cell transplant is equally as effective for patients with multiple myeloma with or without extramedullary involvement. Future studies with long-term follow-up are recommended to further explore these findings. [Table: see text]