Clinicopathological Features of Malignant Lymphoma in JAPAN- Data From the Miyagi Study.

Malignant lymphoma comprises a diverse group of histologic categories. To date, several epidemiological studies in Japan have been reported, however, the data were collected from selected representative institutions, therefore, the results might not reflect the actual incidence and characteristics of malignant lymphoma in Japan. The Miyagi Study is a comprehensive epidemiologic study of malignant lymphoma, including immunologic and genetic information, constructed by a population-based registration system covering Miyagi prefecture, Japan. The population composition by age group and the population growth rate in Miyagi resembles national average figures, therefore, the clinicopathological features of in the Miyagi Study are likely representative of Japan. The purpose of this study was to determine the relative incidences and features of malignant lymphoma subtypes in Japan, compared to that of other countries.

A total of 1546 cases of malignant lymphoma newly diagnosed between 2002 and 2008 in Miyagi prefecture, of which the population is about 2.5 million, were enrolled in the Miyagi Study. Clinical and histopathological data including results of flow cytometry(FCM), immunohistochemistry (IHC), G-banding analysis with or without bicolor fluorescence in situ hybridization(FISH), southern blot analysis with or without polymerase chain reaction(PCR) were collected, and analysed.

The median age of onset was 66 years and the male/female ratio was 1.13. Of the 1546 cases of newly diagnosed malignant lymphoma, 1160 cases (75%) were B-cell lymphomas, 287 cases (19%) were T-cell lymphomas, and only 81 cases (5%) were Hodgkin lymphomas. The most frequent subtype of B-cell lymphoma was diffuse large B-cell lymphoma (DLBCL), accounting for 52% of all B-cell lymphoma cases, followed by follicular lymphoma (FL) and extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma), accounting for 24% and 8% of B-cell lymphoma cases, respectively. The most frequent subtypes of T/NK-cell lymphoma were peripheral T-cell lymphoma, unspecified (PTCLU), angioimmunoblastic T-cell lymphoma(AILT) and adult T-cell lymphoma, accounting for 30%, 15% and 14% of cases, respectively. The relative frequency of malignant lymphoma subtypes was similar to that of Japan reported in 2000 by Lymphoma Study Group of Japanese Pathologists, though there were some differences, such as the high incident rate of FL. There was not a notable time trend in the proportion of FL in B-NHL through 7 years, since it accounted for 20.3% in 2002 and 24.0% in 2008. Within the B-cell lymphoma group, there was a higher frequency of indolent B-cell lymphomas in women (39.8%) compared to men (29.8%). The rates of CD20 and CD22 positivity, as analysed by FCM, were 94.9% and 96.3% in DLBCL, 99.2% and 98.4% in FL, and 98.4% and 100% in MALT lymphoma, respectively. The t(14;18) translocation, a frequent chromosomal abnormality of FL, was present in 63.9% of FL patients, which is less frequent compared with the reports from western countries. De novo CD5+ DLBCL, which is known to have poor outcome, accounted for 21.6% of DLBCL, a frequency higher than previously reported.

The relative frequency of the subtypes of malignant lymphomas in Miyagi is distinct from that of Western countries and shares some similarities with other Asian countries. In the present study, FL was found to be the second largest subtype of malignant lymphoma, consistent with previous reports that FL is increasing in Far East Asia including Japan, Korea and Taiwan. The results of this study reveal the clinicopathologic characteristics of malignant lymphomas in Japan.

No relevant conflicts of interest to declare.