Abstract 5053: Clinicopathologic and molecular genetic features of STAT3-mutated myeloid neoplasms

Abstract STAT3 is a key transcription factor that can mediate cancer progression through phosphorylation or gain-of-function mutations. STAT3 mutations have been mainly associated with large granular lymphocytic T-cell leukemia. Whereas STAT3 activation is common in myeloid neoplasms, it is primarily mediated through STAT3 phosphorylation. STAT3 mutation has only rarely been reported in myeloid neoplasms. We assessed the clinicopathologic and molecular genetic features of 32 STAT3-mutated myeloid neoplasms. Twenty (62. 5%) cases were classified as acute myeloid leukemia (AML), 7 (21. 9%) as myelodysplastic syndrome (MDS), and 5 (15. 6%) as chronic myelomonocytic leukemia (CMML). It is of note that STAT3 mutation was not detected in myeloproliferative neoplasms (MPN). STAT3 mutations were detected at the initial diagnosis in 22 of 25 (88%) cases, suggesting STAT3 mutation is an early event in pathogenesis. However, STAT3 mutations represented the dominant clone in only 6 (18. 8%) cases, all classified as AML. Most are missense mutations, located at the SH2 domain. The median variant allele frequencies were 6. 8%, 4. 6% and 3. 1% for AML, MDS and CMML, respectively, and in a case of CMML, the VAF increased from 2. 4% to 34. 8% upon leukemic transformation. STAT3 mutation was accompanied by co-existing mutations in all cases, with SRSF2 (40. 6%), TET2 (40. 6%), ASXL1 (37. 5%), and SETBP1 (34. 4%) being most common. Cases with STAT3 mutations were usually associated with morphologic dysplasia and increased blasts. Monosomy 7/del7q was the most common cytogenetic abnormality, seen in 11 (34. 4%) cases. With a median follow-up of 24. 5 months, 21 patients died, 6 had persistent disease, and 5 achieved complete remission. We summarize that STAT3 mutation is present in a variety of myeloid neoplasms, but not seen in MPN. It is often an early events and always with concurrent mutations. It may play an important role in the pathogenesis and progression of myeloid neoplasms by activating JAK-STAT pathway, and may serve as a potential therapeutic target. Citation Format: Matthew T. Ye, Zhuang Zuo, Steliana Calin, Fengxi Ye, Hua He, Wataru Kamata, M. James You. Clinicopathologic and molecular genetic features of STAT3-mutated myeloid neoplasms abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5053.