Primary cutaneous diffuse large B-cell lymphoma (PCDLBCL), leg-type and other: an update on morphology and treatment.

Primary cutaneous B-cell lymphoma (PCBCL) is an heterogeneous group of lymphoproliferative disorders, which account for 25-30% of all primary cutaneous lymphoma and include three main histotypes: 1) primary cutaneous marginal zone B-cell lymphoma (PCMZL); 2) primary cutaneous follicular center cell lymphoma (PCFCL); 3) primary cutaneous diffuse large B-cell lymphoma (DLBCL), leg type (PCDLBCL-LT). PCMZL and PCFCL are indolent lymphomas, with an excellent prognosis despite an high rate of cutaneous recurrences; in contrast, PCDLBCL-LT is clinically more aggressive and usually requires to be treated with multi-agent chemotherapy and anti-CD20 monoclonal antibodies. PCDLBCL-LT histologically consists of large round cells (centroblasts and immunoblasts), is characterized by strong bcl-2 expression, in the absence of t(14;18) translocation, and resembles the activated B-cell type of nodal DLBCL. Recently, the term primary cutaneous DLBCL-other (PCDLBCL-O) has been proposed to include diffuse lymphomas composed of large transformed B-cells that lack the typical features of PCDLBCL-LT and do not conform to the definition of PCFCL. Some clinical studies suggested that such cases have an indolent clinical course and may be treated in a conservative manner; however, data regarding the actual prognosis and clinical behaviour of these peculiar cases are still too limited. The spectrum of primary cutaneous DLBCL also encompasses some rare morphological variants, such as anaplastic or plasmablastic subtypes and T-cell rich B-cell lymphoma, and some recently described, exceedingly rare DLBCL subtypes, such as intravascular large B-cell lymphoma and EBV-associated large B-cell lymphoma of the elderly, which often present in the skin.