PPP4C (protein phosphatase 4 catalytic subunit) is a serine/threonine phosphatase with diverse cellular functions centered on DNA damage response and cell cycle regulation. Primary functions include dephosphorylation of key DNA repair proteins—PPP4C dephosphorylates gamma-H2AX and RPA2 to facilitate homologous recombination repair 1, and dephosphorylates PLK1 to negatively regulate its activity during DSB response 1. The enzyme regulates multiple signaling pathways including NF-κB and STAT1 activation 2, and modulates YAP1 activity through MST4 dephosphorylation 3. Clinically, PPP4C overexpression is associated with poor prognosis across multiple cancer types. High PPP4C expression in gastric cancer promotes cell cycle progression by inhibiting p53 signaling, increasing S-phase cells and alleviating G2/M arrest 4. In lung adenocarcinoma, elevated PPP4C correlates with poor survival and promotes tumor proliferation and migration 5. Similarly, high PPP4C expression predicts poor overall and progression-free survival in diffuse large B-cell lymphoma 6. Conversely, PPP4C inhibition sensitizes ovarian cancer to immune attack by activating inflammatory signaling and enhancing NK cell cytotoxicity 2. Non-neoplastic functions include male fertility—PPP4C deficiency causes oligoasthenoteratospermia-like phenotypes in mice 7. These findings position PPP4C as both a prognostic biomarker and potential therapeutic target.