Molecular and immune analysis of adrenocortical carcinoma (ACC): Implications for immune checkpoint inhibition (ICI)

e16617 Background: ACC is a rare and aggressive malignancy. Response rates to ICI are low with scarce yet promising durable responses. Molecular ACC subtypes have been reported based on The Cancer Genome Atlas (TCGA). Here we report the mutational and immune landscapes of ACC obtained from a real-world patient dataset. Methods: DNA (592-gene or whole exome; N=215) and RNA sequencing (whole transcriptome; N=121) were performed for ACC specimens submitted to Caris Life Sciences (Phoenix, AZ). PD-L1+ expression was tested by IHC (SP142; ≥1%). Hierarchical agglomerative clustering (HAC) analysis was performed on a pre-defined set of immune genes. Specimens grouped into immune-high/intermediate (IH) and immune-low (IL) groups. Microenvironmental cell populations (MCP)-counter analysis was used to estimate immune cell infiltrates. Statistical significance was determined using chi-square/Fisher’s exact/Mann-Whitney U tests and adjusted for multiple comparisons (q<0.05). Results: Overall, the most frequent mutations were in TP53 (37%), CTNNB1 (18.7%), ATRX (12.1%), NF1 (9.6%), and RB1 (8.75%), consistent with previous reports. Further, 6.4% of tumors were PD-L1+, 6.1% TMB-high (≥ 10 mut/MB), and 5.9% dMMR/MSI-H. 38.2% of tumors were biopsied from metastatic sites (M). Compared to M, primary (P) specimens had a higher prevalence of TP53 (43.4 vs 26.9%, p<0.05) and TERT promoter mutations (11.1 vs 0%, p=0.08), and a lower prevalence of SMARCB1 (0 vs 3.7%, p=0.054) and BRCA2 (0 vs 3.8%, p=0.056) mutations. Interestingly, M lesions were enriched for HAVCR2 expression (1.3-fold, p<0.05), as well as infiltration of monocytes (1.8-fold, q<0.05) and endothelial cells (1.4-fold, q<0.05). HAC based segregation of tumors based on immune activity was corroborated by a general enrichment of immune cell infiltrates in the IH tumors. IH tumors were enriched for common immunotherapy-related biomarkers (TMB-high, dMMR/MSI-H and PD-L1 positivity), along with a higher prevalence of TP53 and ATRX mutations, while CTNNB1 mutation and CDK4 copy number amplification were less common in IH tumors. Conclusions: Querying a large real-world ACC patient dataset, we find somatic alterations and a low prevalence of ICI-related biomarkers (<10%), consistent with previous reports. Monocyte and endothelial cell infiltration in metastatic tumors suggests an immunosuppressive phenotype compared to primary tumors. Finally, identification of molecular alterations in tumors with distinct immune phenotypes may facilitate development of new therapeutic strategies in ACC. [Table: see text]