PIBF1 (progesterone immunomodulatory binding factor 1) is a multifunctional protein with critical roles in pregnancy maintenance, immune regulation, and cellular processes. During pregnancy, PIBF1 protects against preterm labor by being expressed in decidual B cells in response to IL-33 signaling, where it maintains uterine quiescence and prevents inflammation-induced preterm birth 1. The protein is essential for trophoblast syncytialization and promotes cardiovascular development in the embryo 2. PIBF1 regulates endometrial receptivity through the IL6/STAT3 pathway, with decreased expression in mid-secretory phase associated with recurrent implantation failure 3. Beyond reproduction, PIBF1 functions as a ciliogenesis regulator, with mutations causing Joubert syndrome, a ciliopathy 4. In cancer contexts, PIBF1 displays tissue-specific effects: it acts oncogenically in triple-negative breast cancer by suppressing ATR/CHK1 signaling pathways 5, while paradoxically correlating with better prognosis in breast cancer patients receiving chemotherapy 6. The protein also modulates immune responses by suppressing natural killer cell cytotoxicity in colorectal cancer through enhancer switching mechanisms 7. These diverse functions highlight PIBF1's importance in pregnancy, development, and disease pathogenesis.