Mucinous differentiation in endometrioid adenocarcinomas is not uncommon and pure mucinous adenocarcinomas of the endometrium comprise 1-10% of all endometrioid adenocarcinomas. Most mucin producing tumors of the endometrium are well differentiated with endocervical-type mucin producing cells characterized by tall columnar cells with basally located nuclei. However, the presence of intestinal differentiation, and of goblet cells in particular, within the endometrium is rare. The largest series of endometrial goblet cells differentiation in the world literature reports only two cases, which were identified with the assistance of special stains . Two cases of intestinal metaplasia, one in an endometrial polyp and one in association with complex hyperplasia without atypia, have recently been reported . Neither was associated with endometrial carcinoma, in contrasts to ours. One was associated with concurrent intestinal metaplasia of the endocervical canal. Two cases of endometrial adenocarcinomas with signet ring cells have been reported in the literature  and an additional case of mucinous adenocarcinoma of the endometrium was found to have a gastric phenotype on immunohistochemistry mimicking a minimal deviation adenocarcinoma of the cervix . As in this case, all were associated with more typical appearing endometrioid adenocarcinoma. Enteric-type mucin has been identified in endometrial adenocarcinomas, a finding which verifies the ability of the Mullerian epithelium to undergo metaplasia along an intestinal lineage . No cases in that series, however, showed morphologic intestinal differentiation and there was no correlation with tumor grade.
The presence of goblet cell within the endometrium raises the legitimate question for metastasis. Bland well-differentiated intestinal-type mucinous epithelium with goblet cell in the endometrium, endocervix, and fallopian tubes, has been shown to be metastatic lesions from gastrointestinal primaries . Clinical evaluation for an occult primary gastrointestinal lesion as well as careful gross and histologic exam is necessary. Cytokeratins are useful in this setting as metaplastic Mullerian epithelium retains CK7 positivity, as in our case. In this current case, the patient had no clinical gastrointestinal lesion. The gross exam was that of a classic non-invasive carcinoma arising from endometrial. No involvement of the adnexa, serosa, or the myometrium by the tumor was noted and the cells with intestinal differentiation were intimately associated and readily visible with the endometrioid carcinoma.
Intestinal-type metaplasia is more common within the endocervix, with reports of cases in non-neoplastic and endocervical adenocarcinoma [1, 10]. Intestinal metaplasia in the endocervix is associated with both adenocarcinoma in-situ and endocervical adenocarcinoma and the presence of intestinal-type cells on cervical biopsy warrants further workup.
The etiology of intestinal-type differentiation within the endometrium is unclear. The two recently reported cases associated with non-neoplastic lesions were associated with probable hyperestrogenism , a finding replicated in this patient who was obese and had a background of endometrial hyperplasia. This is in contrast to the proposed mechanism of endocervical-type mucinous metaplasia which has been linked to use of tamoxifen and exogenous progestin [11, 12].
With the addition of our case, the number of cases of intestinal-type differentiation with goblet cells in the endometrium is increased to five, with two cases being benign and two cases associated with adenocarcinoma only detected with special stains [1, 2]. This entity is extremely rare, this being the first case encountered in our sub-specialty practice and consult service.
The clinical implication of finding intestinal-type differentiation in endometrial carcinoma, as in our case report, remains in the fact that the pathologists and clinicians needed to be aware that such differentiation may occur in primary endometrial carcinoma and that the finding of intestinal-type mucinous differentiation in endometrial carcinoma should also warrant careful clinico-pathologic work-up to exclude a metastatic carcinoma from the gastro-intestinal tract.