The tumor microenvironment and infiltrating immune cells are important for cancer biology and progression which has been exploited therapeutically in recent years. 1-3 Whereas infiltrating T cells, macrophages, or natural-killer (NK) cells have been extensively analyzed, recent studies also suggest a role for B cells in cancer biology. 4, 5

Primary cutaneous T-cell lymphomas (CTCL) represent a heterogeneous group of extranodal non-Hodgkin lymphomas of which the most common subtype is mycosis fungoides (MF). At early stages (IIA; EuropeanOrganisationforResearchandTreatmentofCancer [EORTC]/International Society for Cutaneous Lymphomas [ISCL]), MF usually runs an indolent course with almost normal life expectancy. However, advanced-stage MF (IIB), the folliculotropic MF subtype (FMF) and also Sézary syndrome (SS) are more aggressive (median survival, 13-48 months). 6-8 Preclinical data suggest that chronic inflammation promotes CTCL progression with a critical role for macrophages and mast cells. 9, 10 Occasionally, B-cell infiltrations have been reported in CTCL11-14 and although a well-established CTCL model is lacking, B-cell deficient mice exhibited significant regressions of EL4-T-cell lymphoma grafts. 15 Therefore, we analyzed diagnostic skin biopsies of 33 consecutively treated CTCL patients for infiltrating B cells (CD20/CD79a) and reviewed respective clinical data from 1979 to 2011 (Table 1). Psoriasis and eczema tissues served as controls. Staging followed ISCL/EORTC criteria. 16 Lymphoma-tissues containing 50 B-cells/mm2 of lymphoma-infiltrate were assigned as B-cell positive. The study was approved by the institutional review board (No. 08-144).