Background: ACD is a leading cause of mortality in CCS. Previous studies have identified genomic variants that moderate the ACD risk. An agnostic evaluation of differential gene expression between those with and without ACD has not been explored, and could provide insights into the mechanism of cardiotoxicity. Methods:Gene expression profiles in leukocyte RNA from anthracycline-exposed non-Hispanic white (NHW) CCS (20 with ACD [cases]; 20 without ACD [controls]) used Illumina HumanHT-12 v4.0 Expression Beadchips. Gene expression profiles in human iPSC-derived cardiomyocytes (hiPSC-CMs – Day 30) from 6 childhood cancer patients (3 each with and without CD) treated with 1μM doxorubicin or vehicle for 24 h, used RNA-seq. Genotyping in leukocyte DNA from anthracycline-exposed NHW CCS (65 cases; 76 controls) to determine if the differentially-expressed genes mapped to genetic variants that modified ACD risk, used conditional logistic regression analysis adjusted for sex, age at cancer diagnosis, chest radiation and anthracycline dose. Patient characteristics are in Table. Results:Gene-expression in survivors:Glutathione S transferase mu 1 (GSTM1) was differentially-expressed; RT q-PCR showed significant downregulation of GSTM1 in cases (0.67±0.57 vs. 1.33±1.33, p=0.049). hiPSC-CMs gene expression:GSTM1 was downregulated in patients with ACD (logFC = -1.4). Genotyping: Using PCR for GSTM1 null, we observed a significant association between CD risk and GSTM1 null genotype (OR=3.0; 95%CI, 1.4-6.2, p=0.003). Conclusions: We report an association between GSTM1 null genotype and ACD, previously unreported likely because GWAS studies did not examined gene deletions. GSTM1 is involved in detoxification of anthracyclines. This finding could facilitate identification of childhood cancer survivors at increased risk of ACD.