The experience of Japan as a clue to the etiology of testicular and prostatic cancers
Introduction
The incidence of testicular cancer has steadily risen in the past 40 or 50 years in western countries [1], [2], [3], [4], [5]. Prostatic cancer is one the most common cancer among men in most western countries (6). The incidence of both cancers is much higher in western countries than in Asian countries, including Japan (7).
In our previous work (8), we correlated the incidence and mortality rates of testicular and prostatic cancers in 42 countries with the dietary variables in these countries using the cancer rates provided by the International Agency for Research on Cancer (IARC) (7) and the food supply data provided by the Food and Agriculture Organization (FAO) (9). Among the food items examined, cheese was most closely correlated with the incidence of testicular cancer at ages 20–39. The food that was most closely correlated with the incidence of prostatic cancer was milk. The results of the study suggested a role for milk and dairy products in the development and growth of both malignancies.
The common feature of testicular and prostatic cancers in Japan is that the incidence of both malignancies has increased markedly after the end of World War 2. Japan is one of the countries where dramatic lifestyle changes have occurred after the war. For example, as shown in Fig. 1, the consumption of milk and dairy products, meat, and eggs increased 20-, 9-, and 7-fold, respectively, over the 48 years from 1950 to 1998. This great change in the Japanese lifestyle before and after the dividing line of 1945 appears to have affected the incidence of testicular and prostatic cancers. Since the lifestyle changes in Japan are relatively recent and sudden, it is important to examine the experience of Japan as a clue to the etiology of both malignancies.
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Mortality rates of testicular and prostatic cancers
In Japan, there is a working cancer registration system in several regions. However, reliable national data on the incidence of testicular and prostatic cancers are unavailable. In contrast, the death certification system is well established in Japan. Mortality data for testicular and prostatic cancers were gathered from published tabulations of the Vital Statistics of Japan for 1947–1998 (10), in which the data have been organized into 5-year age (age-specific death rate).
The first census of
Testicular cancer
The age-standardized death rate (per million) of testicular cancer in Japan was 0.98 in 1947, increasing rapidly thereafter to reach a maximum rate of 3.49 around 1975, and then decreasing gradually to a low of 1.61 in 1995 (Fig. 2).
The age-specific death rate of testicular cancer in 1961–1970 or later had a characteristic age distribution with peak rates in early childhood (ages 0–4), young adults (ages 20–34), and the elderly (older than 65 years old) (Fig. 3). The peak at ages 0–4, however,
Discussion
The time-related trend in the mortality of any cancer involves relative changes in the diagnosis, recording, and fatality rate of the cancer. The changes in the mortality from testicular cancer in Japan after World War 2 were substantial (Fig. 2). If the changes were due to differences in diagnosis or certification, there must have been a large loss of fatal cases from the recording system in both the 1960s or earlier and the 1980s or later. This is unlikely in Japan, where both health care and
Acknowledgements
This study was supported by a grant from the Ministry of Education, Culture, Sports, Science and Technology (12470083).
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