Abstract A07: Spontaneous canine mammary cancers: A much-needed model for human basal-like breast cancer and an ideal system to understand myoepithelial cells

Abstract

Abstract Spontaneous canine mammary cancer represents an excellent model of human breast cancer but is greatly understudied. To better utilize this valuable resource, we performed the first comprehensive characterization of the genome, transcriptome and epigenome of 12 canine mammary cancer cases, including 7 simple carcinomas and 4 complex carcinomas (1). Simple carcinomas, which histologically match human breast carcinomas, harbor extensive genomic aberrations, many of which faithfully recapitulate key features of human breast cancer. Notably, these tumors closely cluster with human basal-like breast carcinomas from TCGA (2), but not with other intrinsic subtypes, in PAM50 classification with human breast carcinomas. Furthermore, these tumors match the basal-like cancer profile, including MYC amplification, PTEN deletion, BRCA1 mutation, etc. Our results indicate canine simple carcinomas could serve as a much-needed spontaneous cancer model of basal-like breast cancer by effectively bridging the gap between preclinical research and human trials, speeding up drug discovery for the worst subtype of breast cancer. Canine complex carcinomas, characterized by proliferation of both luminal and myoepithelial cells (rare in human breast cancer), appear to lack genomic abnormalities. Instead, these tumors have ~35 chromatin-modification genes downregulated, and are abnormally enriched with active histone modification H4-acetylation while depleted with repressive histone modification H3K9me3. Our findings indicate that these tumors likely originate from epigenomic alterations instead of genomic lesions. Canine complex carcinomas offer an ideal system to study myoepithelial cells, the second major yet significantly understudied cell lineage of the mammary gland.