Features of primary extranodal lymphoma in Kanagawa, a human T-cell leukemia virus type 1 nonendemic area in Japan.

We sought to determine the frequency of primary extranodal lymphoma (ENL) and its characteristics in Kanagawa, a human T-cell leukemia virus type 1 (HTLV-1) nonendemic area in Japan. Subjects were 847 newly diagnosed patients with malignant lymphoma at the Yokohama City University Hospital and 8 affiliated hospitals mainly located in Kanagawa prefecture from 1999 to 2005. We compared the clinicopathological characteristics of primary ENL with primary nodal lymphoma (NL). Histological specimens were evaluated according to the World Health Organization classifications. A total of 395 (46.6%) and 452 (53.4%) patients had primary ENL and primary NL, respectively. The frequency of primary ENL increased with age. Primary extranodal sites included the gastrointestinal tract (30.4%), Waldeyer's ring (17.8%), orbits (7.0%), soft tissue and subcutaneous tissue (5.2%), bone (4.6%), skin (4.3%), thyroid gland (4.3%), testis and prostate (3.3%), bone marrow (3.3%), nasal and paranasal cavities (2.6%), salivary glands (2.3%), lung and pleura (2.0%), breast (1.8%), central nervous system (1.0%), uterus and ovary (0.5%), and others (9.8%). Among the 395 cases of primary ENL, diffuse large B-cell lymphoma (61.2%) was most frequently diagnosed, followed by extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (13.3%) and follicular lymphoma (5.6%). The frequency of primary ENL is approximately 50% of the total lymphoma cases in Kanagawa, an HTLV-1 nonendemic area in Japan. This frequency appears to be higher than that in Western countries.