Granulomatous inflammation of the peritoneum has been described in cases of nonneoplastic conditions, such as fungal or bacterial infections, ruptured dermoid cyst, previous surgical procedure (talc and starch particles) and diagnostic tests (barium and mineral oil) . In 1961, Montes et al. reported a case of well differentiated adenocarcinoma of the uterine corpus with foreign body keratin granulomas, and named it "cholesteatomatous endometriosis" . In 1978, Chen et al. reported five cases of uterine adenoacanthoma with peritoneal foreign body granulomas to keratin . After that, two additional cases associated with an adenosquamous carcinoma and adenoacanthoma of the uterus were reported in 1984  and 1989, respectively .
Histologically, keratin granulomas are composed of eosinophilic laminated keratin surrounded by multinucleated giant cells, histiocytes, lymphocytes and plasma cells. Keratin is associated with ghost squamous cells in which the nuclei have been lost. These keratin materials are speculated to be refluxed from the uterine tumor through the fallopian tubes toward the peritoneum because keratin clumps are often found within the lumen of the fallopian tubes. In addition, many peritoneal keratin granulomas are found around the tubal fimbriae .
It is important to recognize keratin granulomas because they resemble metastatic carcinoma or other granulomatous lesion macroscopically. Microscopically, keratin granulomas may be confused with dissemination, since reactive mesothelial cells near the keratin granulomas may proliferate to form papillary or glandular structures . In peritoneal washing cytology, it may be difficult to distinguish between reactive mesothelial cells and tumor cells. In our case, atypical cells of peritoneal washing were subjected to immunohistochemical stain later. Although they were negative for calretinin and CEA, they were most likely reactive mesothelial cells than adenocarcinoma cells.
Peritoneal keratin granulomas have been reported in cases of endometrioid adenocarcinoma with squamous differentiation of the uterine corpus, ovary, and atypical polypoid adenomyoma [1–9]. To our knowledge, only 24 cases of keratin granuloma with endometrioid adenocarcinoma of the uterine corpus have been reported in the English literature (see Additional File 1). Kim et al. reported four cases with synchronous carcinomas of the endometrium and the ovary; however, we excluded these cases because it is uncertain whether the keratin came from the uterus or the ovary .
In general, the most common location of granulomas in gynecologic specimens is the surface of the ovary, followed by the serosal surface of the fallopian tube. Postoperative treatments including radiation or chemotherapy were performed in 6 of the cases, and twelve cases were treated with only surgery. One case was treated with surgery and intraperitoneal administration of carboplatin. Clinical follow-up is available for 19 cases. Among them, only one case treated with surgery alone showed a recurrence after a 3-years follow-up, but the patient has been free of the disease for further 10 years afterwards . None of the cases died of the disease.
In three cases with endometrioid adenocarcinoma, viable tumor cells were observed in keratin granulomas [2, 6]. These lesions should be regarded as conventional metastatic foci ; however, the prognostic significance has not been confirmed because of the short follow-up period. On the other hand, peritoneal keratin granulomas without viable tumor cells do not influence the staging or the prognosis of the primary carcinoma. Therefore, they should not be regarded as an indicator of metastatic spread [1–4]. Only one case reported that adenocarcinomatous cells were detected by careful pathologic examination in an ovarian endometrioid adenocarcinoma , which suggests that extensive samplings are essential in the evaluation of these cases.