[1084] Well-Differentiated Mucinous “Adenoma Malignum” Adenocarcinoma of the Uterine Corpus: A Rare and Deceptively Bland Form of Endometrial Carcinoma

M Fujiwara, TA Longacre. Stanford University, Stanford, CA

Background: Mucinous epithelial proliferations of the uterine corpus present diagnostic challenges due to their histologic similarity to cervical lesions. We present a distinctive endocervical-like mucinous carcinoma of the uterine corpus resembling adenoma malignum of the cervix that can be mistaken for a benign endometrial process.
Design: The clinical-pathologic features of 16 endometrial carcinomas exhibiting a pure endocervical-type mucinous proliferation, defined as mucin-containing columnar epithelial cells with basal nuclei were evaluated (9 consult and 7 in house files from 2003-2009). Hysterectomy and all available pre-hysterectomy specimens were assessed for architectural complexity (1-3; 3=carcinoma), nuclear pleomorphism (1-3; 3=carcinoma), nucleoli (1-3; 3=carcinoma), nuclear pseudostratification (simulating a villous adenoma), mitotic index, necrosis, and voluminous extracellular mucin (mucin encompassing >50% of a 40X field).
Results: Patients ranged in age from 45-70 years; 7/16 (44%) were postmenopausal. 11/16 (69%) had abnormal bleeding and 7/16 (44%) were receiving, or had been receiving hormonal therapy (1=tamoxifen, 6=estrogen and/or progesterone). Voluminous extracellular mucin was present in 9/16 (56%). Prominent neutrophils were present in 50%. The endometrial sampling specimens were cytologically bland with at most, moderate nuclear pleomorphism and moderate nuclear pseudostratification. With the exception of 2 cases (2/16; 13%), glandular architecture index was low (6/16, 38%) or borderline between low and high (8/16, 50%). A microglandular pattern was not present. Necrosis was seen in 1/16 (6%). On initial pathologic examination, 7/16 (44%) cases were misinterpreted as benign and 4/16 (25%) were classified as borderline. 5/16 (31%) cases were diagnosed as carcinoma prior to hysterectomy. 8/16 (50%) hysterectomies showed myoinvasive carcinoma (3 inner one-half, 5 outer one-half), with extensive lymphovascular involvement in 1/16 (6%) and lymph node metastasis in 1/16 (6%). Three cases had cervical stromal involvement, but a cervical primary was excluded on the basis of bulk of involvement of the corpus and/or negative p16 immunohistochemical stain.
Conclusions: Cytologically bland mucinous epithelial proliferations should be diagnosed with caution in endometrial samplings. The presence of an endocervical-like mucinous epithelial process in association with voluminous extracellular mucin should prompt consideration for a minimal deviation (adenoma malignum-type) mucinous adenocarcinoma of the uterine corpus.
Category: Gynecologic & Obstetrics

Monday, March 22, 2010 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 154, Monday Morning

 

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