OR29-3 Targeted Assessment of G0S2 Methylation Identifies a Rapidly Recurrent, Routinely Fatal Molecular Subtype of Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) is a rare malignancy with frequently dismal prognosis and few therapies. Patients with locoregional ACC routinely receive surgery and adjuvant mitotane, but >50% recur with metastases even after complete resection. Histological grade (Ki67>10% or >20 mitoses/50 HPF) is the strongest clinical predictor of recurrence, but time to recurrence in patients with high grade disease is variable and patients with low grade disease frequently recur. Recent molecular profiling studies suggest risk stratification by DNA methylation may better identify patients with homogenously dismal outcomes; in The Cancer Genome Atlas study on ACC (ACC-TCGA), we similarly identified that patients with tumors bearing CpG island hypermethylation (CIMP-high) exhibit rapid recurrence and early death. However, clinical translation of this complex molecular signature remains challenging. Here, we reanalyzed ACC-TCGA data and show that CIMP-high ACC is characterized by upregulation of cell cycle and DNA damage response programs, and identify that hypermethylation and silencing of G0S2 distinguishes this subgroup. We evaluated G0S2 methylation in a multi-institutional retrospective cohort of treatment-naive primary ACC (n=80) and adrenocortical adenomas (n=22) using a straightforward, overnight restriction digest/qPCR-based assay, validated by targeted bisulfite sequencing. We identified that G0S2 hypermethylation is exclusive to a subset of ACC (40%). G0S2 hypermethylation is associated with decreased disease-free survival (median DFS=14 mo., HR=6.91, p<0.0001; Cox regression) and overall survival (median OS=17 mo., HR=2.65, p<0.005; Cox regression). These observations remain significant in multivariate analyses, demonstrating that G0S2 hypermethylation independently predicts rapidly recurrent and fatal ACC. Our data suggests that prospective targeted assessment of G0S2 methylation may enable clinicians to identify patients with CIMP-high ACC, unlikely to exhibit durable response to standard of care. Ultimately, we hope that improved identification of this subgroup will facilitate the evaluation of more aggressive adjuvant therapies for these patients, and increase patient survival in the face of this devastating disease.