Indolent cutaneous B-cell lymphoma: diagnosis and treatment 2012.

Among primary cutaneous B-cell lymphomas (CBCL), two main clinico-pathologic entities are recognized, i.e. marginal zone lymphoma (MZL), otherwise defined as extranodal MZL, MALT (Mucosa-Associated Lymphoid Tissue) type, and follicle center lymphoma (FCL). They are mostly characterized by indolent course (very limited risk of extracutaneous spread), very good response to non-aggressive treatment (radiotherapy is the gold standard), and excellent prognosis (>90\% 5-year survival overall). The clinical presentation of MZL and FCL slightly differ concerning site predilection (trunk and upper limbs in the former, head&neck and trunk in the latter) and frequency of cases with multiple, non-contiguous lesions (higher in MZL). Histologically, MZL and FCL share the multiphasic evolution of lesions, while some distinctive features are clues to diagnosis and differential diagnosis: CD5-/CD10-/bcl2+ phenotype of neoplastic cells, "colonization" of reactive lymphoid follicles by neoplastic cells, lymphoplasmacytoid and plasma cells at the periphery of nodular infiltrates in MZL; CD5-, CD10 +/-, bcl6+, MUM-1 neg, FOX-P1 neg, IRF4 neg, IgM neg phenotype of neoplastic cells (centrocytes), and neoplastic follicles (in early lesions) in FCL.