Spindle-cell / sarcomatoid SCC
Sarcomatoid SCC; spindle-cell carcinoma; pleomorphic SCC; "carcinosarcoma" of the skin (when biphasic)
Spindle-cell (sarcomatoid) squamous cell carcinoma is a high-grade variant of cutaneous SCC in which the tumour adopts a spindled, sarcoma-like morphology, often with marked nuclear pleomorphism and frequent loss of conventional epithelial differentiation. Diagnostically it is one of the most challenging skin cancers — it must be distinguished from atypical fibroxanthoma (AFX), pleomorphic dermal sarcoma (PDS), leiomyosarcoma, melanoma and angiosarcoma, often only by extended immunohistochemistry (cytokeratin, p63, p40, S100, SOX10, SMA, desmin, CD34, CD31). It usually arises on chronically sun-damaged head, neck or scalp skin of elderly Caucasian patients, frequently within a field of pre-existing actinic keratosis or after prior radiotherapy. Clinically aggressive behaviour with substantial metastatic risk justifies wide excision, sentinel node assessment for selected lesions and consideration of adjuvant radiotherapy.
Clinical features
- Rapidly enlarging, often ulcerated, polypoid or nodular lesion on chronically sun-damaged skin.
- Most common sites: scalp, ear, face, dorsal hand and forearm of elderly Caucasian men.
- Frequently arises within a field of actinic keratosis, prior burn / wound scar, or post-radiotherapy.
- Surrounding sun damage and adjacent low-grade SCC or AK support a diagnosis of sarcomatoid SCC over de novo soft-tissue sarcoma.
- Differential: AFX, PDS, cutaneous leiomyosarcoma, spindle-cell / desmoplastic melanoma, cutaneous angiosarcoma.
Histology & immunohistochemistry
- Sheets and fascicles of pleomorphic spindled and epithelioid cells with brisk atypical mitoses; frequent tumour necrosis.
- Identifying the epithelial origin is the diagnostic challenge — keratin expression is often focal or absent.
- Comprehensive panel:
- Pan-cytokeratin (AE1/AE3, MNF116) — focally positive in 60–70%; sometimes only with a broad cocktail or after extended sectioning.
- p63 / p40 — positive in 60–80%; often the most reliable epithelial marker.
- S100, SOX10, Melan-A, HMB-45 — to exclude spindle-cell / desmoplastic melanoma.
- SMA, desmin, h-caldesmon — to exclude leiomyosarcoma.
- CD34 — to exclude DFSP.
- CD31, ERG — to exclude angiosarcoma.
- If all "specific" markers are negative — the residual differential is AFX (superficial, well-circumscribed, no adverse features), PDS (subcutis invasion / necrosis / LVI / PNI) or cutaneous UPS (deeper extension).
- Search adjacent skin and adjacent epidermis for in situ component or surface SCC, which clinches the diagnosis of spindle-cell SCC.
Management
- Wide local excision with at least 6–10 mm clinical margins; deeper excision (to fascia) for any subcutaneous extension.
- Mohs micrographic surgery for facial / cosmetically important sites.
- Imaging — CT / MRI of the affected region; CT chest/abdomen/pelvis for staging.
- Sentinel lymph node biopsy considered for high-risk lesions (large size, deep invasion, recurrent disease) — emerging evidence base in sarcomatoid SCC.
- Adjuvant radiotherapy for incomplete margins, perineural invasion, named-nerve involvement or multiple positive nodes.
- Cemiplimab (NICE TA802) for advanced / metastatic disease unsuitable for surgery / RT.
- Discussion in skin cancer MDT.
Prognosis
Aggressive — local recurrence 20–40%, regional or distant metastasis 25–35%, 5-year disease-specific survival 50–65%. Worse than conventional well-differentiated SCC of comparable size. Adverse factors include large tumour size, deep invasion, perineural / lymphovascular invasion, immunosuppression (transplant recipients) and recurrent disease. Long-term surveillance for at least 5 years is appropriate.
References
- Henderson SA et al. Sarcomatoid squamous cell carcinoma of the skin — clinicopathologic study. Am J Dermatopathol; 2008.
- Smoller BR. Squamous cell carcinoma — from precursor lesions to high-risk variants. Mod Pathol; 2006.
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