Version May 2024
| Entity | Clinical features | Histology | Immunophenotype | Genetic features/other |
| Primary cutaneous marginal zone lymphoma | Red to violaceous papules, plaques, or nodules localized preferentially on the trunk, upper extremities, or head/neck. Multifocal lesions are common. Ulceration is rare. No evidence of internal or nodal involvement at the time of diagnosis. | Nodular to diffuse infiltrates with sparing of the epidermis. Infiltrate comprised of small to medium sized lymphocytes, often with a plasmacytoid appearance. | Monotypic cytoplasmic immunoglobin (Ig). The neoplastic cells express CD20, CD22, CD79a, and BCL2 and are typically negative for CD3, CD5, CD10, and BCL6. | No single cytogenetic change is typical or diagnostic |
| Primary cutaneous follicle center lymphoma | Solitary or grouped firm erythematous, painless, nonpruritic papules, plaques, or tumors with a predilection for the head, neck, and trunk. Ulceration is rare. No evidence of internal or nodal involvement at the time of diagnosis. | The lesions are composed of predominantly medium-sized and large centrocytes (large cleaved follicle center cells) and variable proportions of centroblasts (large follicle center cells with prominent nucleoli). Growth can be in a follicular, follicular and diffuse, or diffuse pattern. | All cases express pan B cell antigens (CD19, CD20, CD79a), but are usually Ig negative and always CD5 negative. All cases express BCL-6 and most do not express BCL-2. Monotypic surface Ig or surface Ig negative. | No single cytogenetic change is typical or diagnostic |
| Primary cutaneous diffuse large B cell lymphoma, leg type | Red or bluish nodules or tumors on one or both legs, preferentially the lower legs. No evidence of internal or nodal involvement at the time of diagnosis. | Skin biopsy specimens are characterized by a diffuse non-epidermotropic infiltrate, which often extends into the subcutaneous tissue. These infiltrates generally show a monotonous population or large confluent sheets of centroblasts (large follicle center cells with round nuclei and prominent nucleoli) and immunoblasts that spare the epidermis. Frequent mitoses are seen. | The neoplastic cells express B cell markers (eg, CD19, CD20, CD22, and CD79a) and may express cytoplasmic IgM (and IgD) and monotypic Ig light chains. Expression of Bcl-2, Mum1, FOXP1, and MYC proteins are common. Bcl-6 is frequently positive. | MYD88 L265P mutation (60%), and mutations in different components of the B cell receptor signaling pathway, including CARD11 (10%), CD79B (20%), and TNFAIP3/A20 (40%), that all strongly suggest constitutive NF-kB activation |
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