Applications of monoclonal anti-human inhibin alpha subunit in endometrial curettings.

Using archival material, we studied the immunoreactivity and utility of monoclonal anti-human inhibin alpha subunit in the identification of chorionic villi (CV) and trophoblastic subpopulations in endometrial curettings (EC) from patients who had intra-uterine, ectopic, molar and, particularly, probable intra-uterine pregnancies. We also compared its expression with those of betaHCG, HPL and CAM 5.2. The four groups of EC investigated included: Group 1, 15 patients with intra-uterine pregnancies (IUP); Group 2, 15 patients with tubal pregnancies (TP); Group 3, 15 patients with hydatidiform moles (HM); and Group 4, 20 patients with purported history of intra-uterine pregnancies (PIUP). Positive and negative control cases were from Groups 1 and 3 and Group 2, respectively. The test cases were from Group 4. Immunohistochemistry was performed on each case testing for expression of inhibin alpha, betaHCG, HPL and CAM 5.2. Trophoblastic populations, which included syncytiotrophoblast (ST), cytotrophoblast (CT) and intermediate trophoblast (IT), were absent in all 15 negative control cases (Group 2). The 30 positive control cases (Groups 1 and 3) revealed the following: (a) ST, CT and IT were identified in all cases and were positive for CAM 5.2, (b) inhibin alpha, betaHCG and HPL (except one case) were reactive for all cases with ST, but not CT, and (c) IT positivity for betaHCG, HPL and inhibin alpha was 67, 80-93 and 100%, respectively. From the 20 test cases (Group 4), the findings were: (a) CT was absent in all cases, (b) scattered ST cells, which were identified only in 10 cases, were positive for all antibodies, (c) scattered IT cells were present in 17 cases and showed 100% CAM 5.2 positivity, and (d) IT positivity for betaHCG, inhibin alpha and HPL was 58.8% (10/17), 76.5% (13/17) and 82.4% (14/17), respectively. Background staining was observed in 22 of 65 cases (33.8%) stained with betaHCG and HPL; half of these cases came from Group 3. Inhibin alpha and CAM 5.2 staining did not show this problem. We suggest that inhibin alpha is a useful antibody in diagnosing IUP and HM and in documenting intra-uterine gestations in cases with PIUP because it is a sensitive marker in immunolabelling IT and ST. Combined application of inhibin alpha and CAM 5.2 might be more useful than betaHCG and HPL because the latter showed background staining in one third of the cases.