Malignant mixed Müllerian tumor (MMMT) is a rare entity that arises from structures that are embryologically related to the Müllerian system [1, 2]. The usual location of MMMT is the female genital tract. Extragenital origin is extremely rare [3–5]. Histologically and by immunohistochemistry, the tumor exhibits both epithelial and mesenchymal components.

Since the first report in 1955 by Ober and Black [5], to our knowledge there have been only 30 well documented reports of extragenital malignant mixed Müllerian tumors [6–15]. This prompted us to report on a tumor with primary peritoneal location and to review the relevant existing literature.

Malignant mixed Müllerian tumor (MMMT) is a highly aggressive tumor consisted of malignant epithelial and stromal cells. MMMTs were traditionally regarded as a subtype of uterine sarcomas or a mixture of true carcinoma and sarcoma, however several reports suggested a monoclonal origin of these tumors [1–3] Interestingly, molecular data published by Wada and co-workers [4] suggested that although most carcinosarcomas are combination tumors, some develop as collision tumors.

The morphology of the present tumor is consistent with malignant mixed Müllerian tumor. The epithelial component exhibited positivity for cytokeratin 7 and Vimentin and was negative for Cytokeratin 20. Moreover, the mesenchymal component was diffusely positive for Vimentin, focally for CK 7 and exhibited areas of heterologous malignant cartilage.

The primary peritoneal location and origin was confirmed after thorough gross and microscopic examination of the uterus and adnexae. Furthermore, absence of calretinin expression suggested that the tumor was of Müllerian rather than pure mesothelial origin [6]. A search of the literature revealed 30 previously reported cases of extragenital MMMT (Additional file 2) with the majority of the patients being in the postmenopausal age [5–19]. Twenty-two of the reported cases were of primary peritoneal origin and most of them arose in the pelvis [19]. Thirteen were heterologous type [19].

In the homologous type MMMT, mesothelioma would rightfully be considered as a possibility [6]. However, in this case a positive reaction of the cells to Calretinin would be expected [6]. Immunoreactivity of the epithelial cells to Cytokeratin 7 and negative reaction for cytokeratin 20 also points toward Müllerian origin. A theoretical possibility is of course the origin in endometriosis or endosalpingiosis. However, although impossible to rule out, the lack of demonstrable endometriosis associated with the patient's current tumor makes this hypothesis unlikely [16].

Several theories have emerged in the attempt to explain the biphasic appearance of the tumor, the most important of which are the "collision", "conversion" and the "combination" theory [1]. Sternberg et al. [20] was the first to suggest the conversion, stating that sarcomatous elements may develop from carcinoma. They described a case of metastatic heterologous type carcinosarcoma of the omentum with primary endometrial origin. There was no evidence of sarcoma component in the primary tumor. From that time onward, a number of cases with metachronous or synchronous gynaecologic carcinoma have been reported [11, 14, 16]. Masuda et al. [21] further supported the conversion theory with their study in which cell lines established from malignant mixed Müllerian tumors showed the ability of the epithelial tumor cells to transform into epithelial, mesenchymal or both types of differentiation in vitro, while the mesenchymal cells did not show similar capabilities.

MMMT has a poor prognosis with most of the patients following a rapidly fatal course regardless of the initial tumor stage [9]. A review done by Garamvoelgyi et al. [14] showed that most patients passed away within one year with median postoperative survival time being 14 months. Due to the rarity of the disease, limited data regarding the management of peritoneal MMMT exist. Treatment modalities include surgery, chemotherapy and irradiation with various survival outcomes. Ko et al. [19] reported on a patient that was treated with optimal tumor debulking and a combination of chemotherapy with Ifosfamide and Cisplatin, followed by pelvic irradiation. There were no signs of recurrence for 48 months and was the case with the longest disease-free survival in the reported literature.

Based on the ample evidence of the previous reports, and the immunohistochemical analysis of our case, we believe that this is a monoclonal tumor with the carcinoma being the "precursor" element. Nevertheless, further molecular and genetic evidence is needed to support such a conclusion.

Informed consent was obtained from the patient for publication of this case report and accompanying images.