Histopathology immunophenotype and molecular genetics

Histopathology

Histology may show either a patchy perivascular and periad-nexal pattern, or the presence of dense, monomorphous, diffuse or nodular infiltrates of lymphocytes (Fig. 14.4) [4]. The subcutaneous fat is involved as a rule. The tumour is composed predominantly of small lymphocytes without atypical features (Fig. 14.5). Small nodular areas with larger cells

Fig. 14.1 Cutaneous B-cell chronic lymphocytic leukaemia (B-CLL). Nodules on the face conferring the aspect of the so-called 'facies leonina'.

showing features of prolymphocytes or paraimmunoblasts (so-called 'proliferation centres') can be observed occasionally [4]. In some cases, other cells such as eosinophils and epithelioid histiocytes can be found.

In patients with B-CLL, infiltrates of neoplastic lymphocytes may be observed in biopsy specimens of different cutaneous conditions, representing specific manifestations of the disease at sites of skin inflammation caused by different aetiological factors [4,8,9]. A case of cutaneous 'composite' lymphoma with features of both mycosis fungoides and B-CLL has been observed [10], probably representing a further example of the phenomenon just described.

Fig. 14.4 Cutaneous B-CLL. Dense lymphoid infiltrates within the dermis and subcutaneous fat.
  1. 14.5 Cutaneous B-CLL. Monomorphous infiltrate of small lymphocytes.
  2. 14.3 Cutaneous B-CLL. Specific skin manifestation at the site of a Borrelia burgdorferi infection (so-called 'leukaemia lymphatica mamillae').

Immunophenotype and molecular genetics

Immunohistology reveals the presence of B lymphocytes characterized by an aberrant immunophenotype (CD20+, CD5+, CD43+) and monoclonal expression of immunoglobulin light-chains (Fig. 14.6) [4]. CD5 may be negative in some cases. A variable population of reactive T lymphocytes is usually present. Molecular genetics shows in most cases a monoclonal rearrangement of the JH gene.

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