Immunohistochemical and Immunoelectron Microscopic Study of Cytochrome P‐450 of Human Fetal Livers (P‐450HFLa): Implications for an Onco‐Feto‐Placental Enzyme

Cytochrome P-450 of human fetal livers (P-450HFLa) was demonstrated by the avidin-biotin immunoperoxidase technique in tissue samples as follows: human fetal organs, adult livers, human and cynomolgus placenta, and gynecologic organs which were obtained from 40 patients with gynecologic malignancies and 32 patients with benign diseases. P-450HFLa was clearly localized in the cytoplasm and membranes of the hepa-tocytes, and the fact was confirmed by an immunoelectron microscopic examination. In addition, a semiquantitative assay of staining intensity demonstrated that this enzyme, tended to decrease with advancing age. These findings suggest that hepatic P-450HFLa synthesis is inversely proportional to age, and that this enzyme is one of the differentiation antigens. P-450HFLa was also detected immunohistochemically in other fetal organs. The present study thus confirms that P-450HFLa is not specific to the liver and is ubiquitous even in the fetus. Marked positive staining for P-450HFLa was demonstrated in villous syncytiotrophoblasts. In contrast, no positive staining was found in the cynomolgus-monkey placenta, unlike the case for many other placental antigens. These findings lead to the tentative conclusion that P-450HFLa is a feto-placental enzyme peculiar to humans. P-450HFLa was demonstrated to occur very frequently in gynecologic malignancies. The mean positivity rate for all gynecologic malignancies was 85%, while the rate was below 25% for benign gynecologic diseases, indicating that P-450HFLa is one of the onco-feto-placental enzymes. The present study thus suggests that this enzyme could be a promising new tumor marker for gynecologic malignancies.