Cutaneous lymphoma in Japan: a nationwide study of 1733 patients.

Types of cutaneous lymphoma (CL) and their incidences may vary among geographic areas or ethnic groups. The present study aimed to investigate the incidences of various CL in Japan, using epidemiological data from a nationwide registration system for CL. Between 2007 and 2011, 1733 new patients with CL were registered from over 600 dermatological institutes in Japan. The 1733 patients registered included 1485 (85.7%) patients with mature T- and natural killer (NK)-cell neoplasms, 224 (12.9%) with B-cell neoplasms and 24 (1.4%) with blastic plasmacytoid dendritic cell neoplasm. Mycosis fungoides (MF) is the most common CL subtype in the present study (750 patients, 43.3%). The proportion of MF patients with early-stage disease was 73%, similar to that of previous studies from other cohorts. The incidence rates of adult T-cell leukemia/lymphoma and extranodal NK/T-cell lymphoma, nasal type were 16.7% and 2.0%, respectively, which may account for the higher incidence of mature T- and NK-cell neoplasms in Japan, as compared with that in the USA and Europe. A male predominance was observed in most types of CL, except for several CL subtypes such as subcutaneous panniculitis-like T-cell lymphoma.