PB1668 EARLY T‐CELL PRECURSOR (ETP) ACUTE LYMPHOBLASTIC LEUKEMIA (ETP‐ALL) IN ADOLESCENTS AND ADULTS: A HIGH‐RISK SUBTYPE

Background: Early T‐cell precursor (ETP) acute lymphoblastic leukemia/lymphoma (ALL/LBL) is recognized as high‐risk T‐ALL/LBL subgroup. The optimal therapeutic approached to adult patients with ETP‐ALL/LBL not well characterized. Aims: In this study, we compared the outcomes of adults with ETP‐ALL receiving treatment with frontline regimes to those with other T‐ALL immunophenotypic subtypes. Methods: This is a 10 years retrospective analytical study of adult patient diagnosed with T‐ALL. Patients with newly‐diagnosed T‐ALL/LBL receiving frontline chemotherapy between the years of 2008‐2018 at Ampang Hospital, Malaysia were identified and immunophenotypically categorized into TI(pro‐T), T‐II(pre‐T), T‐III (cortical‐T) and T‐IV(mature‐T) as per European Group for the Immunological Characterization of Leukaemia (EGIL) classification using CD1a and cytoplasmic/surface CD3. Overall survival (OS) was analysed using Kaplan‐Meier survival function and different groups were compared using log‐rank test. Event‐free survival (EFS) was calculated from the time of CR until relapse or death. Results: A total of 77 patients with T‐ALL were identified with adequate immunophenotype data. Of the 77 patients, only 60 could be subtyped into Pro‐T (6.7%), Pre‐T (21.7%), Cortical‐T (6.7%), Mature T (23.3%) and ETP (41.7%) subtypes, largely due to discordant expression of differentiation markers that do not conform to this immunophenotypic classification scheme. The ETP‐ALL group had a median age of 29 years, compared to non‐ETP which was 25 years. Among these subtype T‐ALL, 71.7% (n = 43) were age of 35 and above, and 28.3% (n = 17) were below age of 35. There was male predominance (76.7%). Patients were mainly Malay (58.3%), followed by Chinese (21.7%) and Indian (16.7%), with the remaining 3.3% of other racial origins. There was no significant association between total white count (TWC) at presentation and ALL subtypes (ETP vs non‐ETP) using cut‐off of 100 TWC (χ2 = 1.34, df = 1, p = 0.248). This cohort presented median overall survival (OS) of 13 month (95%CI: 9.4; 18.0) and median event free survival (EFS) of 10 month (95%CI: 6.6; 16.4). The majority of patients underwent induction chemotherapy with curative intent (95%, n = 60)whereas 5%(n = 3) were upfront palliative intent. The induction chemotherapy were mainly GMALL or HyperCVAD (93%, n = 57) where less than 10% were BLOCK and BFM (5.3% and 1.8%, n = 6). Median OS and EFS were further evaluated and we found no significant difference among patients of different subtypes, TWC (cut‐off = 100). However, among these factors, TWC appeared to be a potential predictor for OS due to marginal p‐value to 0.05. Summary/Conclusion: ETP‐ALL/LBL represents a high‐risk disease subtype of adult ALL. Novel treatment strategies are needed to improve treatment outcomes of this T‐ALL/LBL subset.