Abstract
Composite lymphomas have been defined as 2 distinct subtypes of lymphoma occurring at a single anatomic site. Composite lymphomas limited to the skin are a rare occurrence and pose a unique challenge. Many reported cases within the skin are combined B-cell and T-cell lymphomas, typically mycosis fungoides and a low-grade B-cell lymphoma. These cases are challenging to recognize because lymphoid infiltrates within the skin often include a mixed population of B cells and T cells. In particular, reactive lymphoid proliferations (pseudolymphomas), primary cutaneous low-grade B-cell lymphomas, and primary cutaneous CD4+ T-cell lymphoproliferative disorder may show nearly equal numbers of B cells and T cells. In order to exclude these possibilities, overwhelming evidence in support of each lymphoma is helpful, including abnormal architecture, cytology, and immunophenotype, as well as molecular genetic evidence of clonality.
Highlights
Man age 70 y with a 10-y history of papular mycosis fungoides (MF) developed a subcutaneous nodule on his right arm that showed a primary cutaneous Composite Lymphomas (CLs)
Woman age 67 y with rheumatoid arthritis (RA) treated for 6 y with MTX and variably with prednisone had a 2-y history of plaques
Man age 73 y with a 2-y history of patch/plaque MF developed plaquelike to nodular lesions on his scalp
Summary
Composite lymphomas have been defined as 2 distinct subtypes of lymphoma occurring at a single anatomic site. Many reported cases within the skin are combined B-cell and T-cell lymphomas, typically mycosis fungoides and a low-grade B-cell lymphoma. These cases are challenging to recognize because lymphoid infiltrates within the skin often include a mixed population of B cells and T cells. 1352 Arch Pathol Lab Med—Vol 142, November 2018 same neoplastic clone (eg, follicular lymphoma transforming to diffuse large B-cell lymphoma).[5–9]. Some authors excluded these latter cases from the term CL, emphasizing the coexistence of 2 ‘‘separate and distinct lymphomas’’ with different cells of origin.[9–11]. 1352 Arch Pathol Lab Med—Vol 142, November 2018 same neoplastic clone (eg, follicular lymphoma transforming to diffuse large B-cell lymphoma).[5–9] Some authors excluded these latter cases from the term CL, emphasizing the coexistence of 2 ‘‘separate and distinct lymphomas’’ with different cells of origin.[9–11] This later definition has gained more support with time
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