Follicular lymphoma in Osaka, Japan: histological features and chronological change.

Follicular lymphoma (FL) is defined as a neoplastic proliferation of follicle center cells with varying follicular areas. To learn the time trend of FL in the Osaka area, an adult T-cell leukemia/lymphoma (ATL) nonendemic area of Japan, we examined the frequency of FL among all non-Hodgkin's lymphomas (NHLs) during the period 1964 to 1987 (n = 1,000) and 1999 to 2001 (n = 659). The frequency of FL with varying follicular areas increased from 1964-1987 to 1999-2001. There was a significant difference in frequency of total cases of FL (14.2% versus 18.8%) (P < .05) and FL with no to 25% follicular area (2.3% versus 5.0%) (P < .01). According to the Berard criteria, cytologic grade of FL was defined by counting the number of centroblasts (CB) in 10 neoplastic follicles as follow: < or = 5 CB per high power field (HPF), grade 1; 6-15 CB, grade 2; >15 CB, grade 3. Immunohistochemical staining with monoclonal antibodies for bcl-2 and CD10 was performed. There was an inverse correlation between follicular area and cytological grade (P < .0001) and bcl-2 expression and cytological grade (P < .01). That is, the larger the follicular area in cases with a lower cytological grade, the stronger was bcl-2 expression in a lower cytological grade. There was a significant correlation between follicular area and stage of disease (P < .05). That is, the follicular area was larger in cases in an advanced stage. This study showed the increase in frequency of FL in Osaka, Japan. Change of lifestyle in Japan may be one of the causative factors for the increase.