The diagnosis of PCDLBCL, LT depends on analyzing skin<unk> iopsies of the involved sites microscopically. These sites show dense,<unk>  sheets of infiltrating large-sized<unk> -cells that resemble centroblasts and immunoblasts. The infiltrates are located in the dermis and subcutaneous tissue<unk> ut, unless there is ulceration, they are separated from the epidermis<unk> y the "grenz zone" i.e. a narrow area of the papillary dermis (i.e. the uppermost layer of the dermis that separates the dermis from the epidermis) that is not infiltrated<unk> y the disease. In addition to the neoplastic<unk> -cells, these infiltrates contain two<unk> s of cells that suppress immune reactions viz., M2 macrophages that express CD163 and myeloid-derived suppressor cells that express PD-L1 and CD33. The sites may also contain poorly differentiated cells;<unk> ut rarely have T-cells, eosinophils, or plasma cells. The lesion's neoplastic<unk> -cells usually have a high proliferative index. Immunostaining these tissues indicates that the neoplastic cells express<unk> -cell marker proteins such as FOXP1 (90% of cases), <unk> cl-2, (90% of cases), IRF4 (85% of cases),<unk> cl-6 (~60% of cases), CD20, CD79a, PAX5, and cytoplasmic IgM. The cells usually do not express CD5, CD10, CD30, or CD138. The neoplastic cells are also usually characterized as<unk> eing of the ABC phenotype as described in the section on the variants of DLBCL, NOS and express the gene abnormalities indicated in the above Pathophysiology section. Patients should<unk> e evaluated for the involvement of non-cutaneous sites<unk> y CT scans of the chest, abdomen, and pelvis, a PET scan, and a<unk> one marrow<unk> iopsy. Individuals who present with an extra-cutaneous DLBCL-like disease should<unk> e diagnosed as having a variant or subtype of DLBCL other than PCDLBCL, LT unless in can<unk> e established that the disease<unk> egan in the skin. Differential diagnosis<unk>  cutaneous follicular center lymphoma differs from PCDLBCL, LT in that its neoplastic<unk> -cells are germinal center<unk> -cells rather than activated<unk> -cells (see Pathophysiology section) that often infiltrate tissues in a follicular (i.e. small spherical groups of cells) rather than<unk>  pattern.<unk>  cutaneous mantle cell lymphoma differs from PCDLBCL, LT in that is neoplastic<unk> -cells appear more like monocytes and/or plasma cells rather than centroblasts or immunoblasts. Intravascular large<unk> -cell lymphoma differs from PCDLBCL, LT in that involved tissues contain large, neoplastic<unk> -cells that are strictly confined within the lumen of small- to medium-sized dermal and subcutaneous<unk> lood vessels.
Primary cutaneous diffuse large B-cell lymphoma, leg type
Secondary cutaneous CD30+ large-cell lymphoma
Primary cutaneous marginal zone lymphoma
Primary cutaneous follicle center lymphoma
Primary cutaneous immunocytoma
CD30+ cutaneous T-cell lymphoma
Non-mycosis fungoides CD30− cutaneous large T-cell lymphoma
Chronic multifocal Langerhans cell histiocytosis