Long-term follow-up of BMT CTN 0702 (STaMINA) of postautologous hematopoietic cell transplantation (autoHCT) strategies in the upfront treatment of multiple myeloma (MM).

8506 Background: STaMINA was a phase III trial comparing progression-free survival (PFS) among 758 pts randomized to: 1. second autoHCT then lenalidomide (Len) maintenance (Auto/Auto, n = 247); 2. consolidation with Len/bortezomib/ dexamethasone (RVD) followed by Len maintenance (Auto/RVD, 254); 3. Len maintenance (Auto/Len, 257). All three arms were similar (Stadtmauer JCO 2018). Len maintenance was designed to continue for 3 years and amended to allow continuation until disease progression through a follow up protocol (07LT, NCT#02322320). We report 6 yr follow up for STaMINA and the results of Len discontinuation beyond 3 years. Methods: 07LT was offered to pts who were progression-free at 38 mo; completed planned Len maintenance and were within 4 years of BMT CTN 0702 follow up. Among 431 07LT eligible patients, 273 enrolled and 179 opted to continue maintenance until disease progression. All patients enrolled in STaMINA were reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) and long-term outcomes for patients not enrolled on 07LT (N = 166) were available through this mechanism. Before combining 07LT data and CIBMTR data for LTFU analysis, outcomes in both databases were analyzed separately and confirmed to be comparable. Results: Using intent-to-treat (ITT), 6yr PFS and overall survival (OS) was the same among Auto/Auto (43.9%; 73.1%), Auto/RVD (39.7%, 74.9%) and Auto/Len (40.9%, 76.4%)(p = 0.6; p = 0.8). Protocol defined high risk disease, (HR = 1.53, p < 0.0001) and age (p = 0.03) were adverse risks for PFS. In as treated analysis, 6yr PFS were 49.4%, 39.7% and 38.6% for Auto/auto (170), Auto/RVD (222) and Auto/Len (361), respectively (p = 0.01). 6yr PFS in high risk pts as treated analysis were 43.6% and 26% for Auto/auto and Auto/Len, respectively (p = 0.03). Landmark analysis at 38 mo included 215 pts who continued Len maintenance (either on 07LT study or commercial Len) vs. 207 who stopped. Baseline demographics; study arm on 0702, induction pre-autoHCT were similar. Len discontinuation after 38 mo was associated with inferior PFS (79.5% vs. 61% at 5yr; HR = 1.91, p = 0.0004) but similar OS. Incidence of all second primary malignancies (SPM)(81 cases with 43 heme-malignancies) was associated with age. Conclusions: Long term outcomes are similar using ITT, but as treated analysis suggested a PFS benefit for tandem autoHCT, driven mainly by pts with high risk MM. Len discontinuation even at 38 mo was associated with inferior PFS. Clinical trial information: NCT02322320 .