Short cases – FGT case 1 (Uterus) – NUS Pathweb

Case writer: Dr Gideon Tan

Clinical history:

55F, with no significant past medical history, presents with repeated post-menopausal per-vaginal bleed.
A CT (computer tomography) scan of the abdomen and pelvis showed a large uterine mass, measuring 16 cm in maximum dimension.
A hysterectomy was performed.
Gross examination of the hysterectomy specimen showed a 15.0 cm mass centred within the myometrium. Cut sections show a pale tan appearance, with areas of haemorrhage and necrosis.
What are the histologic findings?
What are your differential diagnoses?
What ancillary tests would you do?

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Histologic Findings

Differential Diagnoses

Ancillary Tests

The tumour cells show patchy positivity for desmin (a marker of myogenic differentiation)
H-caldesmon and SMA (smooth muscle actin) are also positive. H-caldesmon is a smooth muscle marker, while SMA is a smooth muscle and myofibroblastic marker.

Other ancillary tests performed which were negative:

HMB-45, Melan-A (this excludes a malignant PEComa)

Diagnosis and Learning Points

Diagnosis

Leiomyosarcoma

Learning Points

Adequate sampling is essential to diagnosing a leiomyosarcoma
- The characteristic triad of significant cytologic atypia, high mitotic rate, and tumour cell necrosis may only be identified in certain areas of the tumour. The presence of a high mitotic rate, tumour cell necrosis, as well as widespread (rather than focal) cytological atypia distinguishes leiomyosarcoma from a symplastic leiomyoma.
- Adequate sampling is also key to excluding any heterogenous tumour elements – if a malignant epithelial component is found admixed, the diagnosis is carcinosarcoma.
Leiomyosarcomas can exhibit a range of morphologies
- As seen in this case, leiomyosarcomas can have both spindled and epithelioid cells.
- While nuclear atypia will be present, it is important to remember that the atypia may not be very marked and may be heterogenous within the tumour (again emphasizing the importance of adequate sampling)
- Leiomyosarcomas can also show epithelioid, and myxoid morphologies.
Immunohistochemical stains are supportive but may not always be confirmatory
- PEComas can also demonstrate positivity for smooth muscle markers, and leiomyosarcomas can sometimes be positive for the melanocytic markers which are positive in PEComas.
- Some have proposed certain immunohistochemical stains to help differentiate leiomyosarcomas from benign leiomyomas/symplastic leiomyomas. While supportive, these are often not confirmatory.
- It is important to rely on assessment of morphological features, beyond just immunohistochemistry.

FGT Case 1 (Uterus)