Epidemiology of hypopharyngeal and oropharyngeal cancers in Japan

BACKGROUND: Both hypopharyngeal cancer and oropharyngeal cancer are rare malignancies. However, it is reported that the incidences of these cancers have increased in Japan. It is known that smoking and drinking are risk factors for both cancers. Recently, human papillomavirus (HPV) is regarded as a risk factor for oropharyngeal cancer. In this article the changes in the mortality rates of these cancers are described from the viewpoint of descriptive epidemiology. METHODS: The numbers of deaths due to the 2 cancers from 1979 to 2016 were obtained from the vital statistics of Japan. The numbers of persons in each of the years were obtained from the census and vital statistics of Japan. RESULTS: For males, the ratio of the numbers of deaths from hypopharyngeal cancer/oropharyngeal cancer has been almost constant, at about 2. The crude mortality rate of hypopharyngeal cancer for males has been increasing. The rate in 2016 was about 9 times that in 1979. The male/female ratio has been increasing as well, which is due to the large increase for males and the small increase for females. The crude mortality rate of oropharyngeal cancer for males has been increasing. The rate in 2016 was more than 10 times that in 1979. In the group 50-59 years of age, the crude mortality rate of hypopharyngeal cancer for males has been almost constant. However, in the groups aged 70 years and older, it has been rapidly increasing.  The changes in the crude mortality rates of oropharyngeal cancer were similar to those of hypopharyngeal cancer. In the group aged 50-59 years, the crude mortality rate remained stable. However, in the groups 70 years of age and older, it has been rapidly increasing. The age-adjusted mortality rate of hypopharyngeal cancer for males has been increasing, and there has been no clear sign of a decrease. The age-adjusted mortality rate of oropharyngeal cancer for males has been increasing as well, and there has been no sign of a decrease. While the smoking rate has been decreasing since 1966, the number of cigarettes per smoker per day was increasing during the period from 1960 to 2000. The percentage of heavy drinkers among the population remained almost stable. CONCLUSIONS: For males, since the age-adjusted mortality rates of the 2 cancers have been increasing, it is certain that their incidences have been increasing. Their incidences may largely increase in older age groups. The contribution of the number of cigarettes per smoker to the pathogenesis of these 2 cancers may be larger than that of the smoking rate. The influence of HPV on oropharyngeal cancer was not apparent in the data for mortality rates.