ESR1 and neoplasm: CL1, CL3, and CL4 were almost exclusively found in the primary tumor and represented populations with active stress responses and transcriptional arrest (CL1: high H3K27me3, BCL-xL, p16, pATM, low Ki67), low ERα expression, and elevated phosphorylation of the DNA damage response protein ATR (31) (CL3), as well as a population of mesothelial cells [CL4: Cytokeratins (CKs) and vimentin-high, E-cadherin-low].