P172 | PARTIAL RESPONSE AFTER FIRST TRANSPLANT AND EXTRAMEDULLARY DISEASE ARE NEGATIVE PROGNOSTIC FACTORS IN MULTIPLE MYELOMA PATIENTS UNDERGOING TANDEM STEM CELL TRANSPLANTATION: A MONOCENTRIC EXPERIENCE

Background Autologous stem cell transplantation (ASCT) is a cornerstone in the treatment of multiple myeloma (MM), including tandem ASCT in selected high-risk patients (pts). We retrospectively reviewed our single-center cohort to identify clinical factors impacting progression-free survival (PFS). Methods Clinical data were retrospectively collected from pts’ medical records. Univariate and multivariate analyses were performed using the Cox proportional hazards model, while survival curves were generated using the Kaplan-Meier (KM) method and compared with the log-rank test. Results Among a population of 225 MM pts who underwent ASCT at our center between 2007 and 2023, a total of 127 (56.4%) pts received tandem ASCT based on clinical decision. Seventy-seven pts (60.6%) were male and the median age of the population was 58 years (range 28–69). Induction regimens used were bortezomib-based (n=108, 85%) or daratumumab-based (n=19, 15%). Of these, 57 pts (44.8%) had ISS stage 2 or 3, 12 (n evaluable = 67, 17.9%) had high-risk FISH, and 21 (16.5%) had extramedullary disease. Post-induction responses were very good partial response or better (≥VGPR), partial response (PR) or progressive disease (PD) in 77 (60.6%), 49 (38.6%) and 1 (0.8%) pts, respectively. The median follow-up was 53 months (range 13-215). Cox regression analysis identified only extramedullary disease (EMD) and persistence of PR after the first ASCT as predictors of shorter PFS [univariate: HR 2.0, 95% CI 1.01–3.93, p=0.046; HR 2.05, 95% CI 1.13–3.73, p=0.019; multivariate: HR 1.95, 95% CI 0.99–3.84, p=0.05; HR 1.94, 95% CI 1.05–3.57, p=0.03]. High cytogenetic risk was significant in univariate analysis but was not confirmed in multivariate analysis (p>0.05). All pts with ≥VGPR post-induction maintained or improved their response after the first ASCT (reference group). Among those with PR post-induction (n=49), 22 (44.9%) achieved ≥VGPR post-transplant. KM analysis showed no significant difference in PFS between this group and the reference group [HR 1.14, 95% CI 0.52–2.53, p=0.75]. Conversely, pts who did not improve beyond PR had significantly shorter PFS [HR 2.11, 95% CI 1.12–3.96, p=0.02]. Fig.1. Conclusions In our experience the persistence of PR after the first ASCT and EMD are significant negative prognostic factors in pts undergoing tandem ASCT, independently from cytogenetic risk.