Uterine carcinosarcoma with heterologous osteosarcomatous differentiation: a case report

Uterine carcinosarcoma is a rare biphasic malignant tumor, and the subtype with heterologous osteosarcomatous differentiation is exceedingly uncommon, making preoperative diagnosis challenging. We report the case of a 72-year-old postmenopausal woman who presented with vaginal bleeding. Transvaginal ultrasonography revealed a hypoechoic intracavitary lesion with calcified foci and punctate blood flow signals, and a metallic intrauterine device was also present within the uterine cavity. For diagnostic clarification, the patient underwent hysteroscopic resection of the lesion and removal of the intrauterine device. Histopathological examination and immunohistochemistry supported a diagnosis of uterine carcinosarcoma with heterologous osteosarcomatous differentiation. To exclude a primary bone tumor and further assess local disease extent, the patient subsequently underwent bone scintigraphy and postoperative pelvic magnetic resonance imaging. Final surgical pathology demonstrated residual tumor in the lower uterine corpus with myometrial invasion of less than half the myometrial thickness. According to the FIGO 2023 staging system, the final pathological stage was IIC. After definitive surgery, the patient completed two cycles of adjuvant chemotherapy and one session of radiotherapy, but could not complete the remaining planned treatment because of hematologic toxicity. At the last follow-up on September 23, 2026, no definite evidence of recurrence or metastasis was identified on imaging studies. This case suggests that uterine carcinosarcoma with heterologous osteosarcomatous differentiation should be considered in the differential diagnosis of calcified intrauterine lesions in postmenopausal women with abnormal uterine bleeding. However, such imaging findings are nonspecific, and definitive diagnosis still depends on pathological examination.