Epidemiology of Malignant Lymphoma in Japan

Motoi Nishi


BACKGROUND: Malignant lymphoma (ML) is one of the main malignant neoplasms of hematopoietic organs. In Japan, the number of deaths due to ML is larger than that due to leukemia. Since ML occurs mainly in the elderly, its influences cannot be ignored in Japan, whose society is rapidly aging.

MATERIALS AND METHODS: Data on the crude incidence rates of ML from 1995 to 2015 were obtained from the site of Cancer Registry and Statistics, Cancer Information Service, National Cancer Center, Japan (National estimates of cancer incidence based on cancer registries in Japan, 1975-2015). Data for the numbers of deaths due to ML (ICD10 codes, C81-85) from 1995 to 2016 in 10-year age categories and their age-adjusted mortality rates were obtained from the vital statistics of Japan. The numbers of persons in 10-year age categories in each year were obtained from the census and the vital statistics of Japan. For the statistical test of the correlation coefficient (Pearson), t-distribution was employed.

RESULTS: The incidence rates in all the age groups significantly increased. For both sexes, the entire crude mortality increased, and about 98% of the deaths from ML were accounted for by non-Hodgkin lymphoma (C82-C85, NHL). As age increased, the crude mortality rates of NHL went up. The crude mortality rates of NHL in the groups 50-59 and 60-69 years of age significantly decreased, but the change in the group 70-79 years of age was not significant. Only the crude mortality rates in the group 80-89 years of age increased significantly. Thus, there was a discrepancy between the incidence and the mortality rates.

DISCUSSION: One of the possible factors that can explain the increase in the crude incidence rates of ML is the progress of diagnostic techniques. It is possible, e.g., that the approval use of positron emission tomography led to an increase in detection of patients with ML. The discrepancy between the increasing incidence rates and the decreasing mortality rates for the groups 50-59 and 60-69 years of age might be explained by the prolongation of the survival period through the use of new medications such as rituximab.

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