P770: A COMPARATIVE STUDY OF LEUKEMIC TRANSFORMATION IN THERAPY-RELATED AND DE NOVO MYELODYSPLASTIC SYNDROME AFTER HYPOMETHYLATING AGENT FAILURE

Abstract

Background: Therapy-related myelodysplastic syndrome (t-MDS) is subset of myelodysplastic syndrome (MDS), known for having dismal survival outcomes. The majority of patients (pts) with t-MDS have similar clinical courses with de novo MDS patients after hypomethylating agent failure (HMA-F) that often results in transformation to acute myeloid leukemia (AML). Aims: We conducted a study to identify unique clinicopathologic features of t-AML from t-MDS compared to secondary AML (sAML) from de novo MDS after HMA-F. Methods: We identified sAML patients after HMA-F from all untreated MDS pts in a tertiary cancer center registry from 2017-2021. Clinical characteristics and pathologic data including cytogenetic (CG) and next generation sequencing (NGS) information were collected at the time of MDS diagnosis (dx), HMA-F, and AML dx. Results: 71 (48%) MDS pts with AML transformation after HMA-F were included in the study with a median follow-up time of 15.4 months (mo). At the time of MDS dx, 31 (43%) pts had t-MDS: 97%, 58% and 29% had a history of chemotherapy, radiation, and prior stem cell transplant (SCT), respectively. t-MDS patients were more likely to present with age<65 (48% vs. 28%, p=0.070) and thrombocytopenia (33,000 vs. 75,500, p=0.004) when compared to de novo MDS pts. The majority of t-MDS pts had very high risk disease by IPSS-R (67% vs. 39%, p=0.031), while de novo MDS pts frequently had high risk disease (50% vs. 20%, p=0.013). 90% of t-MDS pts had adverse CG (IPSS-R CG score 3-4) at MDS dx, compared to 46% in de novo MDS pts (p=0.004). NGS at MDS dx showed more frequent TP53 mutations in t-MDS than in de novo MDS (73% vs 36%, p=0.003). Interestingly, ASXL1 (36% vs. 1%, p=0.001), RUNX1 (9% vs. 0%, p=0.004), STAG2 (21% vs. 0%, p=0.013), TET2 (13% vs. 0%, p<0.001), and SRSF2 (18% vs. 0%, p=0.027) were more frequently found in de novo MDS (Table). t-MDS had worse overall survival (OS) from MDS dx (HR 1.82, p=0.026). The median OS from MDS dx was 19.4 mo and 14.3 mo in de novo MDS and t-MDS, respectively. The number of HMA cycles received before HMA-F was 6 (range: 1-13) in t-MDS and 5 (range: 1-23) in de novo MDS. At the time of HMA-F, t-MDS pts presented with more anemia (p=0.005) and thrombocytopenia (p=0.064). The number of CG clones were similar, but the number of CG abnormalities were higher in t-MDS pts (p=0.025). Among pts with subsequent AML transformation after HMA-F, the median time from HMA-F to AML was 1.5 mo in t-MDS to AML, compared to 4.6 mo in de novo MDS to AML. At time of AML dx, 48 (68%) pts had mutation panels available. All TP53 mutation status stayed the same in t-MDS pts at the time of MDS and AML dx. Other changes in mutations were shown in Table. Though the median OS from AML transformation was short in all pts, t-MDS pts had inferior outcomes (2.4 mo vs. 5.0 mo, HR 1.70, p=0.043). The initial response rate to salvage therapy was comparable between t-MDS and de novo MDS after AML transformation (50% and 56%, p=0.761), but more pts underwent SCT with de novo MDS compared to t-MDS (10% vs. 3%, p=0.383). Image:Summary/Conclusion: Transformation to AML after HMA-F results in poor outcomes, but pts with t-MDS have worse survival with distinct CG and mutation profiles. Further understanding of the pathogenesis of AML transformation in both t-MDS and de novo MDS after HMA-F is warranted with improved therapy options an area of unmet need.