HRD can also be caused by defects in the genes involved in homologous recombination repair (HRR), such as ATM. Nowadays, regardless of histological types and anatomic sites, a lot of basket trials are ongoing to evaluate the efficacy of PARP inhibitors on the cancer patients with HRD phenotype, including ATM-deficient cancers and HNC [24,25,26,27,28]. This evidence concerns the gene ATM and cancer.