B-cell lymphoma and lymphocytic leukemia
Cutaneous B-cell lymphoproliferative disorders
Lymphomatoid granulomatosis
B-cell lymphoblastic lymphoma/leukemia
Table 25-1
WHO classification of primary cutaneous B-cell lymphoma
Primary cutaneous follicle center lymphoma
• Most common anatomic site is head/neck (often scalp), followed by trunk
• Composed of neoplastic follicle center cells; i.e. centrocytes and centroblasts in various proportions
• Centrocytes are small with cleaved nuclei
• Centroblasts are larger, with non-cleaved nuclei and 1–3 nucleoli attached to inside of nuclear membrane
• If diffuse growth pattern with sheets of centroblasts, is classified as diffuse large B-cell rather than follicular lymphoma
• Otherwise, numbers of centrocytes and centroblasts do not matter as primary FCL is NOT graded
Primary cutaneous marginal zone lymphoma (Cutaneous MALT-type lymphoma)
• Includes entities previously classified as:
• Primary cutaneous plasmacytoma without underlying myeloma
• Primary cutaneous immunocytoma
• Erythematous to purple nodules/tumors most often on trunk and extremities, often single or few lesions
• Proliferation of small marginal zone centrocyte-like B cells, usually surrounding benign reactive germinal centers
• Immunophenotype: CD20+, CD79a+, BCL-2+, CD5−, CD10−, BCL-6−
• Approximately 70% show evidence of monoclonal light chain restriction
Primary cutaneous diffuse large B-cell lymphoma, leg type
• 80% of cases occur in patients ≥70 years
• Diffuse proliferation of monotonous large transformed B cells
• Activated B-cell immunophenotype, with strong BCL-2+ cells which are MUM-1/IRF4+, CD19+, CD20+, CD79a+, BCL-6 variable
Primary cutaneous diffuse large B-cell lymphoma, other
• Includes intravascular/angiotropic B-cell lymphoma and other non-leg type diffuse large B-cell lymphomas with only skin involvement
Adapted from World Health Organisation Classification of Tumours of Haematopoietic and Lymphoid Tissues, 4th edition, 2008.
Table 25-2
WHO Classification of B-cell Tumors of Hematopoietic and Lymphoid Tissues
Unified system accepted globally by hematopathologists, dermatopathologists, oncologists, other clinicians Formally incorporates previous 2004 WHO-EORTC classification scheme entities
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