Primary cutaneous B-cell lymphoma: a unique type of low-grade lymphoma. Clinicopathologic and immunologic study of 83 cases. The clinical presentation and course, and the morphoimmunologic features of primary cutaneous B-cell lymphoma (CBCL) were investigated in a series of 83 patients. Fifty-one patients were male and 32 were female (male-to-female ratio of 1.6:1); CBCL primarily involved the elderly (median age, 58 years). A locoregional extension of the disease was quite frequent (86.7%). The neoplastic cells showed a range of appearances reminiscent of the whole spectrum of follicular/parafollicular cells. The antigenic phenotype of tumor cells (CD19+, CD20+, CD22+, CD28+, CD10-, CD5-, MB2+, CD74+/-, CDw75+/-, MT2+/-, surface immunoglobulin + monoclonal/-) plus the presence of admixed CD14- dendritic reticulum cells suggest a mantle-zone nature for CBCL. The nonaggressive clinical behavior with a substantial tendency to remain localized to a limited area of the skin, the quite good response to nonaggressive treatment, and the dichotomy existing between the enhancement of morphoimmunologic atypism--which parallels the increasing age and growth rate of lesions--and the constant benign overall prognosis on long-term follow-up make CBCL a unique type of lymphoma of low-grade malignancy. Proper recognition of CBCL is mandatory to avoid possible undertreatment or overtreatment of the patients affected. 