Primary cutaneous follicular helper T-cell lymphoma: a new subtype of cutaneous T-cell lymphoma reported in a series of 5 cases.

BACKGROUND Peripheral nodal follicular T-cell lymphomas expressing follicular helper T-cell (T(FH)) markers have recently been identified. Such lymphomas are characterized by a nodal neoplastic T-cell proliferation accompanied by numerous reactive B cells and demonstrate some overlap with nodal angioimmunoblastic T-cell lymphoma (AITL). We identified 5 cases of cutaneous T-cell lymphoma with a peculiar pathologic aspect and expression of T(FH) markers. OBSERVATIONS The mean age of the patients was 61 years (range, 33-78 years). Four patients had multiple papules, plaques, and nodules predominating on the trunk and the head. One had a nodular plaque on the face. Lesional T-cell clonality was found in all 5 patients, and blood T-cell clonality in 4 of the 5. Nodal involvement was never found. Patients had no systemic symptoms and no biological signs of AITL. In 3 cases, findings from skin biopsy specimens were initially misdiagnosed as primary cutaneous follicle B-cell lymphoma due to major B-cell infiltrate and CD10 positivity. Rituximab-containing therapies were ineffective in these cases, and biopsy specimens after treatment with rituximab showed medium- to large-sized atypical T-cell skin infiltrate expressing T(FH) markers (CD10, Bcl-6, PD-1, CXCL13, and ICOS). The final diagnosis proposed for all patients was cutaneous T(FH) lymphoma. The patient with localized disease was successfully treated with radiotherapy. Patients with diffuse disease showed marked resistance to treatments, with only 1 case of complete remission after allogeneic hematopoietic stem cell transplantation followed by bortezomib and donor-lymphocyte infusion. Bexarotene, methotrexate, thalidomide, interferon alfa, gemcitabine, liposomal doxorubicin, or multiagent chemotherapy with CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) were either ineffective or induced transitory partial remission. CONCLUSIONS We describe an original clinicopathologic series of primary cutaneous lymphomas with T(FH) phenotype, suggesting the existence of a new entity among cutaneous T-cell lymphomas. Relations of these lymphomas with the provisional entity of primary cutaneous small to medium CD4 pleomorphic T-cell lymphoma need to be further addressed.