A monoclonal antibody (MSN-3) was raised using HEC-108 cells derived from poorly differentiated endometrial carcinoma as the immunogen. The immunoglobulin subclass of MSN-3 was IgGr1. The target antigen of MSN-3 was a protein with a molecular weight of 77 kDa, and it was shown to be localized in the cytoplasm. MSN-3 only reacted with 14% of normal proliferative endometrium cells, but it showed a high positivity rate of 66% for endometrial carcinoma. The target antigen of MSN-3 increased as endometrial cells became more malignant, and the possibility of changes in localization was also suggested. Moderately and poorly differentiated endometrial carcinoma showed a high positivity rate for MSN-3. MSN-3 reacted rarely or not at all with normal cervical glandular tissue, but the positivity rate for cervical adenocarcinoma (especially endocervical adenocarcinoma) was a high rate of 59%. The patterns of staining of endocervical adenocarcinoma by MSN-3 included diffuse staining of the whole cytoplasm and not only that near the glandular lumen, as well as staining of the basal cytoplasm. Changes in the localization of the target antigen were clearly associated with carcinogenesis of the cervical glandular cells. The MSN-3-positive rate was high in patients with lymph node metastasis and vascular invasion. Among the staining patterns, the basal and diffuse patterns tended to increase with malignacy. The basal pattern of staining was characteristic of MSN-3, suggesting that it might assist in the diagnosis of cervical adenocarcinoma.

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