L15 – Soft Tissue Tumours: How Rare Entities Are Now a Pilot for the Medicine of Tomorrow Flashcards
What defines “soft tissue” in the context of tumour pathology?
Soft tissue refers to mesenchymal tissues—including adipose, muscle, nerves, vessels, and fibrous tissue—that form the body’s supportive framework.
Besides extremities, where else can soft tissue tumours arise?
They can develop in organs and the skin because these regions contain substantial mesenchymal tissue.
What is the scope of the WHO classification for soft tissue tumours?
It categorises tumours based on differentiation into adipocytic, fibroblastic/myofibroblastic, fibrohistiocytic, vascular, pericytic, smooth muscle, skeletal muscle, chondro-osseous, peripheral nerve sheath tumours, and tumours of uncertain differentiation.
What percentage of benign soft tissue tumours are reported to be superficial?
Approximately 99% of benign soft tissue tumours are superficial.
What size limitation is typical for most benign soft tissue tumours?
About 95% are less than 5 cm in size.
How are soft tissue sarcomas generally distributed in clinical practice?
They are rare; their incidence is low compared to benign counterparts, and they often present with distinct size and depth characteristics.
What constitutes adipocytic tumours?
These are tumours derived from adipose tissue, ranging from benign lipomas to malignant liposarcomas.
What is the most common malignant adipocytic tumour?
Atypical lipomatous tumour, also known as well-differentiated liposarcoma, which accounts for 40–45% of liposarcomas.
What key genetic alteration is associated with well-differentiated liposarcomas?
They characteristically display ring or giant marker chromosomes with amplification of genes (e.g. MDM2) from the 12q13–15 region.
How is dedifferentiated liposarcoma distinguished from its well-differentiated counterpart?
Dedifferentiated liposarcoma occurs in a subset of cases (around 10%) and shows areas of high-grade non-lipogenic sarcoma, often in retroperitoneal sites.
What percentage of adult sarcomas does myxoid liposarcoma represent?
Myxoid liposarcoma represents about 5% of adult sarcomas.
Which chromosomal translocation is most frequently found in myxoid liposarcoma?
The recurrent t(12;16)(q13;p11.2) translocation, resulting in the FUS-DDIT3 fusion gene.
What is the significance of the rare t(12;22)(q13;q12) rearrangement?
It is found in a small percentage (approximately 2%) of myxoid liposarcomas and results in an EWSR1-DDIT3 fusion gene.
What tissue do smooth muscle tumours originate from?
They arise from smooth muscle, which can be found in vessel walls or the erector pili muscles of the skin.
How are cutaneous smooth muscle tumours typically characterised?
They are usually superficial, small, often multiple, and can be painful; some are linked to immunodeficiency and EBV infection.
What is leiomyosarcoma and where is it commonly located?
Leiomyosarcoma is a malignant smooth muscle tumour often found in the extremities, retroperitoneum, and large vessels such as the inferior vena cava.
What diagnostic criteria are used for leiomyosarcoma in soft tissue?
Criteria include mitotic figures per 10 high-power fields, tumour size, depth, and the presence of necrosis, with thresholds varying by site.
What distinguishes a rhabdomyoma from a rhabdomyosarcoma?
Rhabdomyoma is a benign tumour of mature skeletal muscle, whereas rhabdomyosarcoma is malignant and shows immature myogenic differentiation.
Which subtype of rhabdomyosarcoma is most prevalent in children?
Embryonal rhabdomyosarcoma is the most common subtype in the paediatric and adolescent populations.
What histological features are typical of embryonal rhabdomyosarcoma?
They often consist of primitive mesenchymal cells with myogenic differentiation, sometimes positive for MyoD1 or myogenin.
Name some familial syndromes associated with rhabdomyosarcoma.
Syndromes include Costello syndrome, neurofibromatosis type 1, Noonan syndrome, Beckwith-Wiedemann syndrome, Dicer syndrome, Li-Fraumeni syndrome, and Gorlin syndrome.
What is alveolar rhabdomyosarcoma and its associated genetic fusion?
Alveolar rhabdomyosarcoma is a high-grade sarcoma often found in older children and adolescents, with ~60% of cases harbouring the PAX3-FOXO1 fusion gene.
What proportion of alveolar rhabdomyosarcoma cases show the PAX7-FOXO1 fusion?
Approximately 20% of cases have the PAX7-FOXO1 fusion.
What is the primary aim of the 1000 Genomes Project?
To characterise human genetic variation by sequencing whole genomes from diverse populations.
