Clinical overview
Gynaecological sarcomas are malignant tumours of mesenchymal (rather than epithelial) origin. They are uncommon — uterine sarcomas account for only about 3–8% of all uterine malignancies — but they are aggressive, prognostically poor, and clinically treacherous because their commonest presentation, a rapidly enlarging uterus with abnormal bleeding in a peri- or postmenopausal woman, is indistinguishable on history alone from the overwhelmingly more common benign leiomyoma. The clinical importance of this objective for the FCOG(SA) candidate is therefore disproportionate to the rarity of the disease: the registrar who removes "a fibroid" by morcellation and only later receives a histology report of leiomyosarcoma has converted a potentially curable Stage I tumour into disseminated peritoneal disease. The diagnosis is almost always made by the pathologist, not the clinician, so understanding the pathological features — gross appearance, histogenesis, microscopic criteria, immunohistochemistry and increasingly molecular signature — is the core of safe practice.
In the South African context several factors sharpen the problem. Access to expert gynae-oncological histopathology is concentrated in NHLS academic laboratories, so a peripheral specimen may take time to reach a sub-specialist soft-tissue pathologist. Late presentation with bulky disease is common. And the high background prevalence of HIV, while far more relevant to HPV-driven cervical disease, contributes to a population in whom non-HPV malignancies are also seen at younger ages. The pragmatic message is that any "fibroid" behaving atypically — rapid growth, growth after menopause, bleeding out of proportion, degenerate or haemorrhagic appearance on imaging — must be treated as a potential sarcoma until the histology says otherwise. This chapter focuses on the pathology; staging and treatment principles are touched on so the picture is complete, but the diagnostic morphology is the examinable heart of the topic.
Core knowledge
Classification and histogenesis
Figure D11.1 — The uterine sarcomas compared: leiomyosarcoma, low- and high-grade endometrial stromal sarcoma, adenosarcoma and carcinosarcoma — cell of origin and behaviour.
Gynaecological sarcomas are classified by the tissue they recapitulate and by their site, following the WHO Classification of Tumours of the Female Genital Tract, 5th edition (2020). The uterus is by far the commonest site. The clinically and pathologically important entities the registrar must be able to discuss are:
- Leiomyosarcoma (LMS) — malignant smooth-muscle tumour; the commonest uterine sarcoma (roughly 60–70% of cases).
- Low-grade and high-grade endometrial stromal sarcoma (LGESS / HGESS) — arising from endometrial stroma.
- Undifferentiated uterine sarcoma (UUS) — a high-grade tumour lacking specific differentiation, a diagnosis of exclusion.
- Adenosarcoma — a mixed tumour with benign epithelium and malignant (sarcomatous) stroma.
- Carcinosarcoma (malignant mixed Müllerian tumour, MMMT) — now reclassified by WHO 2020 as a metaplastic/dedifferentiated carcinoma, NOT a true sarcoma. It is included here because exams still test the distinction; biologically it behaves and is treated as a high-grade, often serous-like, epithelial carcinoma.
Beyond the uterus, vulvar and vaginal sarcomas are rare; embryonal rhabdomyosarcoma (sarcoma botryoides) is the classic vaginal sarcoma of infancy and young childhood, presenting as a grape-like haemorrhagic polypoid mass. Ovarian sarcomas are very rare and usually arise within a carcinosarcoma or teratoma.
Leiomyosarcoma — gross and microscopic features
Figure D11.2 — Leiomyosarcoma vs benign leiomyoma: the Stanford criteria (atypia, ≥10 mitoses/10 HPF, coagulative tumour-cell necrosis), STUMP, and the morcellation hazard.
Gross. A leiomyosarcoma is typically a single, large (often >10 cm), softer, fleshy mass with a variegated cut surface showing necrosis and haemorrhage, frequently with an ill-defined, infiltrative margin rather than the crisp shelling-out plane of a benign fibroid. The classic benign leiomyoma, by contrast, is firm, whorled, white and well-circumscribed. These gross clues are exactly why specimens that look unusual at theatre should be sent for urgent histology and why power morcellation of an undiagnosed mass is hazardous.
Microscopic. The diagnosis of uterine LMS rests on the Stanford triad of three features, of which at least two are required:
- Significant cytological atypia (diffuse, moderate-to-severe nuclear pleomorphism).
- High mitotic count — conventionally ≥10 mitoses per 10 high-power fields.
- Tumour-cell (coagulative) necrosis — geographic necrosis with an abrupt transition from viable tumour to dead cells, distinct from the gradual hyalinised infarct-type necrosis seen in degenerating fibroids.