Purpose: To determine if an immunomodulatory protein (progesterone induced blocking factor [PIBF]) that is progesterone induced and found in higher concentration during pregnancy is similarly found with increased levels in women with gynecologic cancers. Materials and Methods: A newly developed enzyme linked immunoabsorbent assay (ELISA) assay was used to measure PIBF in the sera of six women with various gynecologic cancers and compare them to five controls (three with benign tumors and two having gynecologic procedures for non-tumors. Results: The PIBF levels in women with gynecologic cancer did not rise precipitously as historical controls of women or men exposed to progesterone. The two highest PIBF levels of the 11 subjects were in women with gynecologic cancer. Conclusions: The data suggest that if PIBF helps cancer cells to evade immune surveillance, it probably operates through an intracytoplasmic presence. If an increase in sera PIBF could have been detected in women with gynecologic cancer, then this ELISA test could have been used to detect tumor recurrence. Future studies may concentrate on evaluating intracytoplasmic PIBF to possibly help determine which tumors may respond to progesterone antagonist receptors.