4th June 2025

Diagnosis

CBCL presents with skin changes including papules, nodules, plaques and tumours. They can range in colour from pink/red to blue/purple. PCFCL and PCMZBCL are often found on the upper extremities, trunk or scalp, whereas PCDLBCL-LT is generally found on the legs.

If CBCL is suspected from the history and examination, a skin biopsy is required for diagnosis; this must be sufficiently deep and include the subcutaneous fat. Histological and cytological examination of the biopsy will be performed, plus immunohistochemistry.

• Primary cutaneous follicle centre lymphoma:
  • Histology/cytology – accumulation of germinal centre B-cells (centrocytes and centroblasts) in the dermal and subcutaneous tissues, these form a follicular growth pattern.
  • Immunohistochemistry is positive for B-cell antigens (e.g. CD19, CD20 and CD22).
  • It is negative for the chromosomal t(14;18) translocation – which is found in generalised follicular lymphoma. This is helpful to distinguish PCFCL from follicular lymphoma that has spread to the skin.
• Primary cutaneous marginal zone B-cell lymphoma:
  • Histology/cytology – infiltration of the dermis with marginal zone B-cells (and other immune cells) in a nodular or diffuse pattern.
  • Immunohistochemistry is positive for B-cell antigens CD79a, CD20 and Bcl-2.
  • Blood tests for Borrelia burgdorferi may be performed, given its association with PCMZBCL.
• Primary cutaneous diffuse large B-cell lymphoma, leg-type:
  • Histology/cytology – dermal and subcutaneous fat infiltrates of centroblasts and immunoblasts (B-cell precursors), these may form a sheet pattern.
  • Immunohistochemistry is positive for B-cell antigens CD79a, CD20 and IgM.
  • Bcl-2 and MUM1 expression is significant for PCDLBCL-LT.
• The presence of palpable lymphadenopathy indicates extra-cutaneous involvement and the need for further imaging – such as a CT or PET-CT scan.