Cutaneous Spindle-Cell B-Cell Lymphomas: Most are Neoplasms of Follicular Center Cell Origin

Cutaneous lymphomas of both B cells and less commonly T cells can exceptionally exhibit spindle-cell morphology. Less than 30 spindle-cell B-cell lymphomas of the skin have been described, mostly before the adoption of detailed immunohistochemistry, and thus initially interpreted as variants of diffuse large B-cell lymphoma (DLBCL). Furthermore, some authors suggest that cutaneous spindle-cell B-cell lymphomas (cSCBCLs) may behave more aggressively than their conventional morphologic counterparts and may thus merit more aggressive treatment. Herein we describe the largest case series of cSCBCL analyzed to date to characterize their clinicopathologic and immunohistochemical features and clarify their subtype according to the current WHO/EORTC classification scheme. Twenty-four cSCBCLs arose in 18 male and 6 female individuals with a mean age of 55 years, mostly on the head (12/24), trunk (8/24), and lower extremities (4/24). Histopathologic features were similar for all cases. Neoplasms involved the entire dermis and focally the subcutis. The neoplastic infiltrates comprised a mixture of medium-sized, visually prominent spindled cells (15%; up to 85% of the infiltrate) arranged in a fascicular pattern around nodular aggregates and admixed in a random manner between centrocyte/centroblast-like cells within these nodular collections. Immunohistochemical support for a follicular center cell origin was present in 22/24 cases, 1 was consistent with DLBCL-leg type and 1 defied precise classification, best fitting with intermediate-grade DLBCL-other. Our findings reinforce the concept that most cSCBCLs are variants of low-grade B-cell lymphomas of follicle center cell origin and not intermediate-grade variants of DLBCL.