Cutaneous leiomyosarcoma
"Atypical smooth muscle neoplasm (cutaneous)" / superficial leiomyosarcoma — modern descriptors of the dermal subtype following Kraft & Fletcher 2011; the term "atypical intradermal smooth-muscle neoplasm" appears in some literature but is not the formal WHO 5th-edition designator
Cutaneous leiomyosarcoma is a smooth-muscle sarcoma originating from arrector pili (dermal subtype) or vascular smooth muscle (subcutaneous subtype). The two subtypes behave very differently: the dermal subtype — described as atypical smooth muscle neoplasm in current WHO 5th-edition descriptive practice (Kraft & Fletcher 2011 terminology) — is indolent with very low metastatic risk and good outcomes following wide local excision. Subcutaneous leiomyosarcoma is a true sarcoma with substantial metastatic potential (30–40%) and worse prognosis. Recognition of the distinction guides margin width, sentinel lymph node consideration and surveillance intensity.
Subtypes & classification
- Dermal (atypical intradermal smooth-muscle neoplasm) — confined to the dermis; arises from arrector pili muscle. Indolent. Local recurrence reported up to ~30% with inadequate excision but low with clear margins; metastasis <5%.
- Subcutaneous — extends into / arises within subcutis; vascular smooth-muscle origin. Aggressive. Metastasis 30–40%; metastatic spread to lung most common.
- The descriptive term "atypical smooth muscle neoplasm" (Kraft & Fletcher 2011) reflects the benign clinical course of the dermal subtype; this is the practical working terminology used by UK histopathologists rather than a formal WHO 5th-edition designator.
Clinical features
- Slowly enlarging, firm, often tender or pruritic dermal/subcutaneous nodule.
- Most common on the lower limb (~60%) and trunk; head and neck less so.
- Median age 50–70; M>F (2:1).
- Skin colour change, ulceration or fixity to deeper tissues are late features.
- Often misdiagnosed as cyst, lipoma, dermatofibroma or BCC.
Histology
- Interlacing fascicles of spindled cells with eosinophilic, fibrillar (smooth-muscle) cytoplasm and cigar-shaped nuclei.
- Variable cytological atypia and mitoses; tumour necrosis is a high-grade feature.
- Smooth muscle actin (SMA), desmin and h-caldesmon positive; S100 negative.
- Differential: cellular dermatofibroma, atypical fibroxanthoma, spindle-cell SCC, melanoma.
Management
- Dermal subtype: wide local excision with 1 cm clinical margin; Mohs micrographic surgery for facial sites with comparable outcomes.
- Subcutaneous subtype: wide local excision with 2 cm margin including deep fascia; sarcoma MDT involvement.
- Imaging: MRI of the affected region for subcutaneous disease; CT chest for staging.
- Sentinel lymph node biopsy not routinely performed; nodal metastasis is uncommon.
- Adjuvant radiotherapy for incomplete margins or high-grade subcutaneous disease.
- Systemic therapy for metastatic disease — doxorubicin, ifosfamide, gemcitabine-docetaxel; trabectedin in selected patients.
Prognosis
Dermal: 5-year overall survival >95%. Subcutaneous: 5-year overall survival 50–60%, with metastatic disease the main cause of death. Long-term surveillance is important — particularly for subcutaneous lesions where late metastasis is well described.
References
- Fields JP, Helwig EB. Leiomyosarcoma of the skin and subcutaneous tissue. Cancer; 1981.
- WHO Classification of Soft Tissue and Bone Tumours, 5th edn; 2020.
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