We noted a number of similarities between the AT3 tumors and prostate carcinosarcomas, including their undifferentiated histology, mesenchymal-like gene expression profiles,17 aggressive nature and preference for metastasizing to the lungs and lymph nodes.24 Indeed, AT3 cells resemble the more poorly differentiated component of human carcinosarcomas in their histopathology (Supplementary Figure S6A), their likely epithelial origin and weak to negative co-expression of epithelial biomarkers, such as cytokeratin, and expression of vimentin (Supplementary Figure S6B). Here, VIM is linked to carcinosarcoma.