TNKS2 and neoplasm: While PARP5B downregulation has been observed in prostate, breast, and HNCs [167,168], recent data demonstrate that null PARP5B tumor cells are characterized by an impairment of the NHEJ mechanism, and that treatment with a PARP5B inhibitor combined with low doses of etoposide drives SCC human cell lines into senescence and apoptosis [169].