Distribution of malignant lymphomas in the anterior mediastinum: a single-institution study of 76 cases in Japan, 1997-2016.

We analyzed the distribution of tumors and lymphomas of the anterior mediastinum diagnosed between 1997 and 2016 at the National Cancer Center Hospital, Japan. The median age of 283 patients with anterior mediastinal tumors was 48 (range 6-84) years, and 143 (51%) were male. The incidence of tumors was as follows: thymoma, 34%; thymic carcinoma, 16%; primary mediastinal large B-cell lymphoma (PMBL), 13%; germ cell tumors, 10%; classical Hodgkin lymphoma (CHL), 9%; thymic cyst, 7%; metastatic tumors, 3%; T lymphoblastic leukemia/lymphoma (T-LBL), 2%; other lymphomas, 3%; and others, 3%. Of the newly diagnosed lymphomas in 60 patients, PMBL (46%) was the most frequent, followed by CHL (32%), T-LBL (12%), mucosa-associated lymphoid tissue lymphoma (3%), and other lymphomas (7%). These findings suggest a recent increase in PMBL in Japan. The frequency and subtype of lymphoma differ with age and sex. In female patients ≤40 years old, 58% of the anterior mediastinal tumors were PMBL (39%) or CHL (19%). Germ cell tumors were the most frequent in male patients ≤40 years old, followed by CHL (21%), PMBL (17%), and T-LBL (10%). This distribution may serve as a reference for routine histologic diagnosis of lymphomas in the anterior mediastinum in Japan.