Carcinosarcoma, also known as malignant mixed Müllerian tumor (MMMT), represents a distinct pathological entity. It is a malignant tumor combining sarcomatous and carcinomatous components [1] - [3] . Historically classified as a Müllerian tumor, recent changes in its classification have complicated bibliographic research.

The origin of carcinosarcomas remains debated, with two main hypotheses: one suggests a totipotent stem cell that differentiates into both epithelial and mesenchymal components [4] , which is the most likely, while the other postulates the coexistence of two independent cellular populations. These tumors were long considered uterine sarcomas, but their prognosis is now known to depend primarily on the carcinomatous component. They are currently classified as epithelial tumors of endometrial origin.

Histological analysis suggests that carcinosarcomas resemble epithelial metaplasia and derive from a single clone [5] . This could explain why their prognosis, lymphatic dissemination, and overall disease behavior are similar to those of carcinomas.

We report a case of uterine carcinosarcoma initially diagnosed as high-grade serous carcinoma.

A 75-year-old woman, G5P5, with a history of atrial fibrillation managed with rivaroxaban and hypertension treated with bisoprolol, presented with abnormal uterine bleeding one week prior to consultation.

Gynecological examination revealed a polyp prolapsing through the cervix. Pathological analysis suggested high-grade serous carcinoma.

MRI revealed irregular endometrial thickening infiltrating more than 50% of the myometrial thickness and extending to the cervical canal, classified as FIGO stage II as shown in Figure 1 .

Based on the staging and histology, total hysterectomy with bilateral salpingo-oophorectomy, omentectomy, peritoneal biopsy, and pelvic and para-aortic lymphadenectomy were planned.

Intraoperatively, carcinomatosis was discovered. The surgical procedure included total hysterectomy with bilateral salpingo-oophorectomy, infracolic omentectomy, peritoneal biopsy, and peritoneal cytology as shown in Figure 2 . Pathological analysis revealed a carcinosarcoma with heterogeneous tissues, reclassified as FIGO stage IIIB.

The patient was treated with palliative chemotherapy (paclitaxel and carboplatin) but succumbed to the disease seven months post-surgery.

Carcinosarcoma is a malignant mixed Müllerian tumor combining a mesenchymal malignant component with an epithelial carcinomatous component [6] as shown in Figure 3 .

Although historically considered a uterine sarcoma, its prognosis is now understood to depend primarily on the carcinomatous component. These tumors are currently classified as endometrial epithelial neoplasms [7] [8] .

Carcinosarcomas predominantly affect postmenopausal women and typically present as abnormal genital bleeding [9] [10] , as observed in our patient.

Clinical and radiological evaluations often underestimate disease extent [11] . In this case, the initial diagnosis was high-grade serous carcinoma based on a cervical polyp analyzed in a peripheral laboratory. MRI classified the tumor as FIGO stage II, but intraoperative findings of carcinomatosis upgraded the disease to FIGO stage IIIB. Subsequent pathological analysis confirmed carcinosarcoma, a more aggressive entity that explains the rapid progression.

Uterine carcinosarcoma, also referred to as malignant mixed Müllerian tumor, is a rare and highly aggressive neoplasm predominantly affecting postmenopausal women. Combining carcinomatous and sarcomatous components, its prognosis remains poor due to its aggressive nature and advanced stage at diagnosis.

This case highlights the challenges of early detection and the critical role of a multidisciplinary approach in managing this complex pathology.