This review considers the pathologic features of
endometrioid carcinoma of the uterine corpus, which accounts for approximately 80% of endometrial
adenocarcinomas, with an emphasis on its histologic features, recent advances, and problematic aspects. In addition to typical
endometrioid carcinoma, the variants of
endometrioid carcinoma covered include secretory
carcinoma, villoglandular
endometrioid carcinoma,
endometrioid carcinoma with small nonvillous papillae,
endometrioid carcinomas with microglandular and sertoliform patterns, and
endometrioid carcinomas with metaplastic changes. These changes include a variety of different appearances of squamous epithelia (ranging from mature and keratinizing to immature with only subtle evidence of a squamous nature), clear cells, surface changes resembling syncytial
metaplasia or microglandular
hyperplasia, ciliated cells, oxyphilic cells, and spindled epithelial cells (sarcomatoid
carcinoma). The last is one of several variants that may cause a biphasic appearance, all of which should be distinguished from the malignant müllerian mixed
tumor. Rare findings in
endometrioid carcinomas include hyalinization, psammoma bodies, and foci of stromal
metaplasia such as osteoid. Unusual growth patterns of
endometrioid carcinomas include involvement of
adenomyosis, the "diffusely" infiltrating pattern of myoinvasion, and a previously unemphasized pattern of myoinvasion with "pinched off" glands that may be cystic or have a pseudovascular appearance, often with a myxoid stromal reaction. Other aspects of
endometrioid carcinoma discussed are its immunoprofile, grading, cervical involvement (including a hitherto undescribed "burrowing" pattern of extension within the cervix that can result in underdiagnosis of stage IIB disease),
carcinoma arising in the lower uterine segment,
carcinoma arising in
polyps and
adenomyomas,
carcinoma in young women,
tamoxifen-related
carcinoma, associated ovarian
endometrioid carcinoma, and peritoneal
keratin granulomas. Finally, the differential diagnosis of
endometrioid carcinoma is briefly considered with a section on benign mimics, including
curettage-related changes, menstrual changes,
adenomyosis-related problems, metaplastic changes, atypical polypoid
adenomyoma, radiation atypia, and papillary proliferations, and a section on metastatic colonic
carcinoma.