Incidence Rate, Subtype Frequency, and Occurrence Site of Malignant Lymphoma in the Gastrointestinal Tract: Population-Based Analysis in Miyagi, Japan.

Primary gastrointestinal lymphoma (PGIL) has been reported in many studies of lymphomas of the gastrointestinal tract worldwide. However, there have been few accurate population-based reports on lymphomas, and it is difficult to apply the strict definition of PGIL to all lymphomas occurring in the gastrointestinal tract. Accordingly, instead of using PGIL, this study included newly diagnosed lymphomas with biopsy or excision specimens obtained from the gastrointestinal tract (GI-related lymphomas) and aimed at presenting the incidence rate, subtype frequency, and occurrence site of GI-related lymphomas. Additionally, we examined GI-related lymphomas diagnosed using flow cytometry (FCM) analysis, cytogenetics analysis, and molecular analysis (multimetric and/or integrated analysis). We extracted data on GI-related lymphomas from 2,098 lymphoma cases registered from the entire Miyagi Prefecture in Japan. The number of GI-related lymphomas was 350, and the incidence rate was 2.97 per 100,000 persons. Diffuse large B-cell lymphoma was the most common subtype (47.4%), followed by extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (32.6%) and follicular lymphoma (8.3%). The stomach was the most common site (62.6%), followed by the large intestine (15.4%), small intestine (14.3%), and duodenum (6.0%). Of the 350 included cases, 111 were diagnosed using multimetric and/or integrated analysis, in which the proportions of positive results for FCM analysis, cytogenetics analysis, and molecular analysis were 81%, 33%, and 51%, respectively. These results may provide a representation of lymphomas occurring in the gastrointestinal tract in Japan. Multimetric and/or integrated analysis of GI-related lymphomas could enable us to acquire useful information for the diagnosis.