Applying the new TNM classification system for primary cutaneous lymphomas other than mycosis fungoides and Sézary syndrome in primary cutaneous marginal zone lymphoma

Background: Primary cutaneous marginal zone lymphoma is recognized as a unique subset of low-grade cutaneous B-cell lymphoma with indolent course in the current World Health Organization-European Organization on Research and Treatment of Cancer classification system. However, few large series on this entity have been reported, including the new TNM (tumor, (lymph) node, metastasis) classification for non-mycosis fungoides cutaneous lymphomas. Objective: We aimed to characterize the clinical features including new TNM classification for non-mycosis fungoides cutaneous lymphomas, as well as outcomes and responses to therapy in 30 patients with primary cutaneous marginal zone lymphoma. Results: Primary cutaneous marginal zone lymphoma typically presents with deep-seated nodular or papular lesions on the upper extremities or trunk (25/30). Disease course is indolent and none of 30 patients died of disease. Sustainable complete remissions were obtained only in patients with T1a (n = 3) and T2a (n = 1) disease. Most patients have persistent stable disease independent of treatment. Two patients developed systemic disease and 5 developed large cell transformation. Limitations: The average follow-up time was 63 months (range, 3-204 months). Longer follow-up time is needed to determine whether patients with untreated persistent stable disease are at greater risk relative to patients treated aggressively early in the disease course. Conclusions: Primary cutaneous marginal zone lymphoma is a distinct subtype of marginal zone lymphoma with an indolent disease course. Patients with T1a or T2a disease (ie, single lesions or a localized cluster of lesions) may achieve sustained complete remission, whereas patients with multiple nonlocalized lesions are unlikely to maintain complete remission independent of treatment modality. Systemic involvement is typically preceded by large cell transformation and may be an indication for more systemic therapy. Death from disease is rare.