ATM and neoplasm: Conversely, germline and somatic ATM aberrations are common in metastatic prostate cancer; ATM functions as a cell cycle checkpoint, preventing cell cycle progression in the presence of DNA damage rather than directly mediating repair, unlike BRCA2 and PALB2. In the TOPARP-A trial, five patients had ATM aberrations in tumour biopsies: two of these had a PSA response, and two more had circulating tumour cell conversion.