title: Apparent resistance in human endometrial carcinoma during combination treatment with tamoxifen and progestin may result from desensitization following downregulation of tumor progesterone receptor.
abstract: Combined treatment with tamoxifen and progestin effectively controlled human endometrial tumor growth in the nude mouse model. However, after an initial response the tumors became 'resistant' to continuous progestin administration. Tumors excised during the growth arrest or regrowth phases, showed return of the typical growth characteristics of EnCa-101, upon serial transplantation. The characteristic progesterone receptor proteins were observed by Western blot analysis in tamoxifen treated tumors, while tumors treated with both tamoxifen and progestin were devoid of receptor, beginning at 7 days after initiation of progestin therapy. Thus, downregulation of endometrial tumor PR resulting from continuous progestin administration presumably leads to desensitization to progestin, after an initial growth inhibitory response.
authors.affiliation: Department of Obstetrics and Gynecology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
authors.forename: P G
authors.initials: PG
authors.lastname: Satyaswaroop
authors.forename: C L
authors.initials: CL
authors.lastname: Clarke
authors.forename: R J
authors.initials: RJ
authors.lastname: Zaino
authors.forename: R
authors.initials: R
authors.lastname: Mortel
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002277:Carcinoma / Q000737:chemistry / Q000188:drug therapy* / Q000473:pathology; D002455:Cell Division; D015536:Down-Regulation; D004351:Drug Resistance; D016889:Endometrial Neoplasms / Q000737:chemistry / Q000188:drug therapy* / Q000473:pathology; D005260:Female; D008297:Male; D008525:Medroxyprogesterone / Q000008:administration & dosage / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011980:Receptors, Progesterone / Q000032:analysis / Q000378:metabolism*; D013629:Tamoxifen / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D011980:Receptors, Progesterone; D013629:Tamoxifen; D008525:Medroxyprogesterone