PARP9 and Familial prostate cancer: 15). In addition, PARP9 has been found as part of a trimeric complex with DTX3L and PARP14, regulating proliferation, survival and chemo-resistance in metastatic prostate cancer cells, in a way dependent on STAT1 activation (Ref. 16). Similarly, PARP9/DTX3L also control the AR-mediated transcription in prostate cancer cells (Ref. 17). A similar role for PARP9 has been recently reported in head–neck squamous cellular carcinoma (HNSCC), where PARP9 forms a complex with PARP14 and DTX3L to promote survival signals (see below and (Ref. 18)).