Characteristics and prognosis of mutated STAG2 myeloid neoplasms.
Authors: Katamesh Bahga , Nanaa Ahmad , He Rong , Viswanatha David , Nguyen Phuong L. , Greipp Patricia T. , Gangat Naseema , Begna Kebede , Mangaonkar Abhishek Avinash , Patnaik Mrinal , Hogan William J. , Litzow Mark Robert , Shah Mithun Vinod , Arana Yi Cecilia Ysabel , Foran James M. , Badar Talha , Alkhateeb Hassan B. , Al-Kali Aref 
Published: June 2022

e19014 Background: Stromal Antigen 2 ( STAG2), located on Xq25, is the most mutated (m) cohesin-complex gene in myeloid neoplasm (MN) patients (pts). mSTAG2 is present in around 5% of MN and has been linked to secondary AML and potential poor impact on outcome. Methods: We retrospectively screened MN pts who had next-generation sequencing (NGS) (OncoHeme) performed at Mayo Clinic between 2018-2021. m STAG2 pts were included at the date of NGS. Charts were reviewed for clinical information after obtaining IRB approval. BlueSky Software V7.40 was used for statistical analysis. Results: Characteristics: 70 pts with mSTAG2 MN were identified, their median age was 72 years (range 25-91); with 55 pts (79%) being males. Complete blood counts showed median white blood cell count of 2.8 x109/L, hemoglobin of 8.9 gm/dL and platelets of 89 x109/L. The diagnosis was MDS in 38 pts (54%), AML in 20 (29%), MDS/MPN in 9 (13%), MPN in 2 (3%), and CCUS in 1 (1%). 11 cases (16%) were defined as therapy-related MN (tMN). Cytogenetics were normal in 45 pts (64%) and abnormal in 22 (31%). 10/50 non-AML pts progressed to AML (after median time of 9.8 months). Hematopoietic cell transplantation (HCT) was done in 20 pts (29%). mSTAG2: median VAF (mVAF) was 50% (range, 5%-100%). Males had higher mVAF compared to females (64% vs. 27%, p= .001), and tMN pts had higher mVAF compared to de novo (dn) MN pts (66% vs. 43%, p= .03). mVAF had no correlation with disease classification (50% in AML, 52% in MDS, 41% in MDS/MPN, 36% in MPN and 5% in CCUS, p= .5). STAG2 mutations were nonsense, frameshift, and splice site in 50%, 37%, and 13%, respectively. Co-mutations : median number of co-mutations was 3 (range, 0-6). Most common co-mutations were ASXL1 (66%), SRSF2 (37%), TET2 (36%), RUNX1 (29%), IDH2 (21%), BCOR (20%) and U2AF1 (16%) while least common were TP53, SETBP and ZRSR2 (1% each). Neither number (p= .08) nor type of co-mutation correlated with MN classification. There was no difference in the co-mutational pattern between tMN and dnMN pts. Survival : median overall survival (mOS) was 16.3 months with a median follow up time of 24.5 months. Pts who received HCT had better OS compared to non-HCT pts (mOS not reached vs. 14.9 months, p= .003). Pts with an isolated m STAG2 had better OS than co-mutated pts (p= .04), while the type of STAG2 mutation did not affect OS (p= .3). Pts with tMN had worse OS than dnMN pts (9.9 vs. 20.4 months, p= .02). VAF ≥75% had a negative impact on OS (20.5 vs 8.1 months, p= .008). mOS did not differ based on MN diagnosis. On multivariate analysis, only HCT (HR 0.3, p= .01) and VAF ≥75% (HR 2.3, p= .02) had impact on OS. Conclusions: mSTAG2 was more common in elderly males and MDS diagnosis. mSTAG2 was uncommon as an isolated mutation, indicating a possible role in disease progression with preferred certain co-mutations ( ASXL1/SRSF2/RUNX1/IDH2). mOS was poor regardless of MN diagnosis indicating a molecularly driven significance of an aggressive disease. The study needs to be validated by larger studies.