Sarcomas may arise from any mesenchymal tissue in the body; in the uterus those that arise from the endometrial stroma are of different origin and follow a different course to the myometrial sarcomas. There are three grades:
- Endometrial stromal nodule (benign)
- Endometrial stromal sarcoma (low grade)
- Undifferentiated endometrial sarcoma (high grade)
The benign and low grade lesion resemble proliferative endometrial stroma; ESS bears no such resemblance.
Endometrial stromal sarcomas are very uncommon, making up less than 5% of malignancies arising from the endometrium. They may occur at any age but often ten years earlier than the peak incidence of carcinomas.
Aetiology and Pathogenesis
Exact aetiology is unknown.
Many sarcomas have a particular fusion of two 'zinc finger' genes, JAZF1 and JJAZ1; this is caused by a translocation t(7;17). The resulting protein has anti-apoptotic functions in the cell.
Low grade tumours tend to extensively invade the uterus before developing metastatic disease. Higher grade tumours metastasise widely and lead to death within several years, even with hysterectomy.
Patients present with menorrhagia or post-menopausal bleeding; those with advanced stages may present with signs of metastatic disease. Anaemia may be present. MRI and transvaginal ultrasound can help to evaluate the extent of disease.
Endometrial stromal nodules usually present as such with pushing margins; low grade endometrial stromal sarcomas are often more diffuse in their spread. Undifferentiated endometrial sarcomas are characterised by multiple masses with haemorrhage and necrosis visible to the naked eye.
Nodules and low grade sarcoma have a similar microscopic pattern, with spindle cells similar to the endometrial stroma. Margins on the endometrial stromal nodule are pushing whereas those for the low grade sarcoma are infiltrative. Low grade ESS possesses a vasculature resembling the spiral arteries of the endometrium. Immunohistochemistry is usually positive for vimentin but not for desmin.
Undifferentiated sarcoma consists of atypical cells that bear no structural resemblance to the lower grade lesions. The margins are pushing as opposed to infiltrative. There is no recapitulation of the typical endometrial spiral arteries. Differentiation from a low grade lesion is based on nuclear pleomorphism and necrosis. Immunohistochemistry shows high Ki-67 levels (over 10%) and lack of hormonal receptors.
Staging / Classification
Staging is similar to other endometrial tumours.
- Uterine Malignancy
WHO Classification of Tumours