Uterine sarcomas comprise less than 1% of gynecologic malignancies and 2% to 5% of all uterine malignancies. The following tumors arise primarily from three distinct tissues:
Carcinosarcomas arising in the endometrium, in other organs of mullerian origin, and accounting for 40% to 50% of all uterine sarcomas.
Leiomyosarcomas arising from myometrial muscle, with a peak incidence occurring at age 50, and accounting for 30% of all uterine sarcomas.
Sarcomas arising in the endometrial stroma, with a peak incidence occurring before menopause for the low-grade tumors and after menopause for the high-grade tumors, and accounting for 15% of all uterine sarcomas.
The three distinct entities are often grouped under uterine sarcomas; however, each type of tumor is currently being studied in separate clinical trials.
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Carcinosarcomas (the preferred designation by the World Health Organization [WHO]) are also referred to as mixed mesodermal sarcomas or mullerian tumors. Controversy exists about the following issues:
Whether they are true sarcomas.
Whether the sarcomatous elements are actually derived from a common epithelial-cell precursor that also gives rise to the usually more abundant adenocarcinomatous elements.
The stromal components of the carcinosarcomas are further characterized by whether they contain homologous elements, such as malignant mesenchymal tissue considered possibly native to the uterus, or heterologous elements, such as striated muscle, cartilage, or bone, which are foreign to the uterus. Carcinosarcomas parallel endometrial cancer in its postmenopausal predominance and in other of its epidemiologic features; increasingly, the treatment of carcinosarcomas is becoming similar to combined modality approaches for endometrial adenocarcinomas.
Other rare forms of uterine sarcomas also fall under the WHO classification of mesenchymal and mixed tumors of the uterus. These include:[2,3]
Mixed endometrial stromal and smooth muscle tumors.
Adenosarcomas, in which the epithelial elements appear benign within a malignant mesenchymal background.
Embryonal botryoides or rhabdomyosarcomas, which are found almost exclusively in infants.
PEComa-a perivascular epithelial-cell tumor that may behave in a malignant fashion, which is the latest to be added.
(Refer to the PDQ summary on Childhood Rhabdomyosarcoma for more information.)
The only documented etiologic factor in 10% to 25% of these malignancies is prior pelvic radiation therapy, which is often administered for benign uterine bleeding that began 5 to 25 years earlier. An increased incidence of uterine sarcoma has been associated with tamoxifen in the treatment of breast cancer. Subsequently, increases have also been noted when tamoxifen was given to prevent breast cancer in women at increased risk-a possible result of the estrogenic effect of tamoxifen on the uterus. Because of this increase, patients on tamoxifen should have follow-up pelvic examinations and should undergo endometrial biopsy if there is any abnormal uterine bleeding.[4,5,6]