Defects in the DNA repair system lead to a predisposition for developing cancer. At least some of the PIAS proteins are implicated in DNA repair, and specifically in enhancing repair of double-stranded breaks. In cell culture, overexpression of PIAS3 demonstrated an increased resistance of HeLa cells to ionizing radiation. This indicates a significant role for PIAS3 in DNA repair. Additionally, overexpression of PIAS3 inhibited human lung cancer cell growth in vitro and rendered cancer cells up to twelve times more sensitive to chemotherapeutic drugs. While inhibition of PIAS by siRNAs led cancer cells to accelerate cell proliferation and demonstrate higher levels of resistance to chemotherapy drugs. In a study of human brain tissue samples from glioblastoma multiforme patients, PIAS3 expression was found to be reduced compared to the control brain tissue. Inhibition of PIAS3 resulted in increased glioblastoma propagation, while PIAS3 overexpression inhibited STAT-3 signaling and cell proliferation . Furthermore, patients with higher levels of BRCA1, PIAS1, and PIAS4 survived for a longer period of time in a retrospective study of advanced gastric cancer patients.