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) . 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
showing features of prolymphocytes or paraimmunoblasts (so-called 'proliferation centres') can be observed occasionally . 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 , probably representing a further example of the phenomenon just described.
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) . 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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