Primary cutaneous anaplastic large cell lymphoma (pcALCL)

Definition

pcALCL is a rare, usually indolent cutaneous T-cell lymphoma composed of large, CD30-positive atypical lymphocytes. Together with lymphomatoid papulosis, it belongs to the primary cutaneous CD30-positive lymphoproliferative disorders and is the second most common cutaneous T-cell lymphoma after mycosis fungoides.

Occurrence & epidemiology

Men are affected about three times as often as women; most patients are 50–70 years old. Paediatric and congenital cases have been reported.

Aetiopathogenesis

The cause is unknown. About 30% of tumours carry a rearrangement of the DUSP22 gene (6p25.3).

Clinical features

• Usually a rapidly growing solitary nodule or plaque, red to violaceous, typically at least 2 cm in size and often ulcerated; usually asymptomatic.
• Multiple grouped or generalised nodules in about 20%.
• Any skin region including mucosal surfaces can be affected, most often the upper half of the body.
• No systemic symptoms (no fever, weight loss or night sweats).
• Partial or complete spontaneous regression in 20–40% after a median of 2 months; extracutaneous involvement, mostly of lymph nodes, in about 10%.

Histology

Diffuse dermal infiltrate of medium to large anaplastic or pleomorphic cells with abundant cytoplasm and horseshoe-shaped nuclei, with no or only focal epidermotropism, sometimes extending into the subcutis. At least 75% of tumour cells are CD30-positive; a clonal T-cell receptor gene rearrangement is found in 60–100%.

Diagnosis

• Skin biopsy with histology and immunohistochemistry.
• Dermoscopy: peripheral branching and polymorphous vessels on a pink-yellow structureless background.
• Staging (blood count, LDH, CT and/or PET-CT; TNM classification) to distinguish systemic ALCL with skin involvement.
• Lymphomatoid papulosis often cannot be distinguished on histology alone.

Differential diagnoses

• Primary cutaneous anaplastic large cell lymphoma
• Mycosis fungoides
• Primary cutaneous aggressive epidermotropic CD8-positive cytotoxic T-cell lymphoma
• Dermatofibrosarcoma protuberans
• Atypical fibroxanthoma
• Cutaneous angiosarcoma
• Basal cell carcinoma
• Dermatofibroma

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References (selection)

1. DermNet: Primary cutaneous anaplastic large-cell lymphoma
2. Primary Cutaneous Anaplastic Large Cell Lymphoma-A Review of Clinical, Morphological, Immunohistochemical, and Molecular Features
3. Primary cutaneous anaplastic large-cell lymphoma: a review of the SEER database from 2005 to 2016

Cross-references