12540 Epigenetic Subtyping Of Adrenocortical Carcinoma In Archival Material And Implications For Disease Evolution

Abstract Disclosure: D. Mohan: None. A.M. Lerario: None. M.Q. Almeida: None. B.B. Mendonca: None. A. Latronico: None. M.C. Fragoso: None. G.D. Hammer: None. Adrenocortical carcinoma (ACC) is a rare cancer of the adrenal cortex, to date cured only by surgery. Pangenomic studies demonstrate that ACC is comprised of three molecular subtypes with distinct clinical outcomes. CIMP-high ACC, the most aggressive molecular subtype, is defined by abnormal epigenetic patterning including inappropriate DNA methylation. CIMP-high status of the primary tumor accounts for 30% of all ACC, but 70% of metastatic relapses. It remains unclear if ACC transitions molecular subtypes, e.g. acquires CIMP-high status, during metastatic dissemination. We and others have demonstrated that G0S2 methylation is a sensitive and specific single-locus biomarker capturing CIMP-high ACC. However, our prior studies utilized frozen tissues, often only available at specialized centers. Here, we measured G0S2 methylation in an expanded cohort of n=73 formalin-fixed paraffin-embedded (FFPE) primary, recurrent, and metastatic ACC samples. We show that G0S2 methylation status is stable in archival FFPE material, concordant with measurement in frozen specimen (Pearson r=0.94, n=28). We identify that, within individual patients, the G0S2 methylation status of the primary is often preserved in the metastasis or recurrence. These data suggest that ACC subtype switching is not required for metastatic evolution. In cases of advanced ACC with accessible lesions amenable to biopsy, epigenetic subtypes can be diagnosed prior to oncologic resection, enabling subtype-specific therapeutic interventions in the neoadjuvant setting. Presentation: 6/1/2024