Endocrine Abstracts

Adrenocortical carcinoma (ACC) is an aggressive cancer, with, in its advanced stages, a median 5-year survival rate of less than 15%. ACC is rare in humans, but in dogs the incidence is at least 100 times higher. Because these dogs receive medical care, have an intact immune system, and have inter-individual and intratumoral heterogeneity, the dog is a unique spontaneous animal model to study new treatment options for ACC. However, to determine similarity of canine and human ACCs, a more in-depth analysis is required. We therefore sequenced the whole transcriptome of 36 canine cortisol-secreting adrenocortical tumors. Bulk RNA was sequenced with the CEL-seq method to produce paired-end 75 base long reads, and reads were aligned to the canFam3 reference genome. After quantification, reads were converted to reads per kilobase of transcript per million reads sequenced (RPKM). Statistics included the Log Rank test for survival analysis and the independent t-test for differences between groups. The tumors were previously classified as either low risk of recurrence tumors (LRT; n = 13) or moderate-high risk of recurrence tumors (MHRT; n = 23) based on our newly developed histopathological Utrecht score (a canine variant of the Weiss score). However, in principal component analysis, these groups did not cluster apart. Unbiased clustering analysis divided the tumors into two main groups: 1 and 2. Survival analysis showed that group 2 had a significantly shorter estimated median survival time after adrenalectomy (30 ±5 months) than group 1 (74 ± 7 months) (P < 0.0001). Significantly upregulated genes in group 2 included several genes also known to be upregulated in human ACCs when compared to adrenocortical adenomas, e.g., TOP2A, PTTG1, CDC2, and ASPM. In addition, genes differentially expressed between the groups included genes important in adrenocortical development such as SHH, but also genes not previously linked to adrenocortical development or tumorigenesis such as CCDC33, HK2, and CYP26B1. The results of this study greatly increase our understanding and improve the classification of canine adrenocortical tumors. This brings valuable insight into how comparable canine ACCs are to human ACCs, and for which treatment targets dogs with spontaneous ACC are a suitable animal model. In addition to previously identified factors in adrenocortical tumorigenesis, these results identify new factors that not only improve our understanding of ACC, but could also be targeted therapeutically.