Benign tumourSarcoma mimicICD-10 D17.x
Spindle cell / pleomorphic lipoma
SCL · pleomorphic lipoma · SCL/PL · pseudoangiomatous spindle cell lipoma
Spindle cell and pleomorphic lipomas are benign adipocytic tumours within a spectrum sharing a characteristic 13q14 deletion (RB1 / RCBTB2 / FOXO1 region). They classically present as slow-growing subcutaneous nodules on the posterior neck, shoulders or upper back of middle-aged or older men. The principal clinical relevance is as a benign mimic of liposarcoma — particularly atypical lipomatous tumour and pleomorphic liposarcoma — and recognition prevents over-treatment.
CurrentLast reviewed 22 May 2026
Epidemiology
- Adults 40-70 years.
- Male predominance (~9:1).
- Posterior neck, shoulder, upper back — "shawl distribution" classical.
- Solitary; rarely multiple.
- Slow growth over years; usually painless.
Pathology
- Composed of mature adipocytes, bland spindle cells, mast cells and ropy collagen.
- Spectrum from "pure" spindle cell lipoma to pleomorphic lipoma with multinucleated "floret" cells (giant cells with peripheral wreath-arranged nuclei).
- 13q14 deletion / monosomy with loss of RB1, RCBTB2 and FOXO1-region material — shared with mammary-type myofibroblastoma and cellular angiofibroma.
- IHC: CD34+ (spindle cells), Rb loss; S100 negative in spindle cells (positive in adipocytes); MDM2 / CDK4 negative — distinguishes from atypical lipomatous tumour.
- No atypia, no mitoses, no necrosis.
Clinical features
- Soft to firm, mobile, subcutaneous nodule.
- 1-5 cm diameter typically; can grow larger.
- Sites: posterior neck (commonest), shoulder, upper back; rarely cheek, scalp, oral.
- Asymptomatic; rarely tender.
- Overlying skin normal.
- Slow growth.
Differentials
- Lipoma (ordinary) — softer, more lobulated, less characteristic site.
- Atypical lipomatous tumour / well-differentiated liposarcoma — deeper, larger, MDM2 / CDK4 amplification.
- Pleomorphic liposarcoma — high-grade; necrosis; atypia.
- Angiolipoma — tender; numerous small lesions.
- Hibernoma — brown-fat composition.
- Solitary fibrous tumour — CD34+; STAT6+; NAB2-STAT6 fusion.
- Dermatofibroma / dermatofibrosarcoma protuberans — different architecture; DFSP COL1A1-PDGFB.
- Mammary-type myofibroblastoma — shares 13q14 deletion.
Investigations
- USS: well-defined hyperechoic mass with internal echoes.
- MRI: characteristic fat-suppressed pattern; differentiates from liposarcoma (intermediate signal in non-fat areas raises concern).
- Excisional biopsy for definitive diagnosis.
- Pathology with IHC (CD34, Rb, MDM2, CDK4); molecular (13q14 FISH) if uncertain.
Management
- Excision: complete local excision with thin margin is curative.
- Recurrence rare with complete excision.
- No metastatic potential.
- No need for adjuvant therapy.
- Counsel patient about benign nature and excellent prognosis.
- Pathological clarification mandatory — sarcoma exclusion always required.
References
- Enzinger FM, Harvey DA. Spindle cell lipoma. Cancer. 1975;36:1852-1859.
- Shmookler BM, Enzinger FM. Pleomorphic lipoma. Cancer. 1981;47:126-133.
- WHO Classification of Tumours Editorial Board. WHO Classification of Soft Tissue and Bone Tumours, 5th ed. Lyon: IARC; 2020.
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