Cancer Letters 90 (1995) 75-79

CANCER LETTERS

Epidemiology of breast cancer in Japan

Suketami Tominaga* a, Tetsuo Kuroishi b ‘Airhi Cancer Center Research Institute. I-I, Kanokoden, Chikusa-ku, Nagoya, 464, Japan

bDivision of Epidemiology, Nagoya, Japan

Accepted 1 December 1994

.^._ ---~---_ .-___- II

Abstract

-

The mortality and incidence of breast cancer are high in Western industrialized countries and relatively low in developing countries in Asia and other parts of the world. In Japan the mortality of breast cancer has gradually been increasing, but is still much lower compared with that of Western countries. Within Japan the mortality of breast cancer is higher in urban areas than in non-urban areas. The future estimation of cancer incidence in Japan predicts that breast cancer will become a leading cancer in the near future.

Keywords: Breast cancer; Epidemiology; Mortality; Incidence; Japan ~.---“_.^-..l_l_^

1. International comparison of the breast cancer mortali@

Breast cancer is one of major cancers in females. The mortality and incidence of breast cancer are high in western industrialized countries and relatively low in developing countries in Asia and other parts of the world. Fig. 1 shows the time trends of the age-adjusted mortality of breast cancer from 1953-1957 to 1983-1987 for selected countries in the World [ 11. The mortality of breast cancer has stabilized in countries where the mor- tality was high and has been increasing in coun-

* Corresponding author, Tel.: +81 52 76261 I1 (Ext. 8800); Fax: +81 52 7635233.

tries where the mortality was low. A marked increasing trend of breast cancer mortality can be observed in Czechoslovakia and Spain. The mor- tality in Japan has gradually been increasing, but is still low.

2. Trends in the breast caocer mortality ad related factors in Japan.

According to the vital statistics in Japan [2], over the past 30 years (1960- 1990), the number of deaths has increased 3.47 times and the crude death rate of breast cancer has increased 2.69 times, whereas the age-adjusted mortality of breast cancer has increased only moderately (1.61 times). Fig. 2 shows the age-specific death rates for 1960, 1970, 1980 and 1990. An increasing trend is more

0304”3835/95BD9.50 0 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3835(94)03680-H

76 S. Tominaga, T. KuroishilCancer L.etiers 90 (1995) 75-79

Female

( 4 U.K.,England 8 Wales

1953-57 1958-62 1963-67 1968-72 1973-77 1978-82 1983-87

Year

Fig. I. Trends in the age-adjusted death rate of breast cancer for selected countries (1953-1957 to 1983-1987). Data source: Kuroishi et al. (1994) [l).

markedly observed for the age groups of 50-70 years old.

To study the possible reasons for the increasing trend of breast cancer mortality in Japan, trends of several factors possibly related to the cause of breast cancer were examined. According to the vital statistics in Japan [3], the number of children has been decreasing and the average age of the

mother at the birth of the first child has been in- creasing; both of which are compatible with an increase in breast cancer. Among environmental risk factors, diet, especially high fat/calorie intake is regarded as an important risk factor of breast cancer. Fig. 3 shows the relative trends in selected food and nutrient intake in Japan. A marked in- creasing trend is observed for meat, milk and fat

S. Tomiuaga, T. Kuroishil Cancer Letters 90 (1995) 75-79 77

! I i: i: i: .

Cltles with dlfbmnt population ah@ thousands)

Fig. 4. Age-adjusted death rates of breast cancer in five areas with different population size in Japan (1981-1983). Data source: Kato et al. (1987) [4].

0 I

.lIII/!II/III

30 40 50 60 70 80 90

Age in years

Fig. 2. Trends in the age specific death rate of breast cancer in Japan (19HLi990). Data source: Kuroishi et al. (1994) [2].

intakes, whereas the caloric intake has been stable over the last 35 years. Thus, it is likely that fat in- take, especially of animal origin, has contributed much more to the increase of breast cancer in Japan than caloric intake. Kato et al. further examined the chronological relations between the

B Vitamin C

1955 1960 1965 1970 1975 1980 1985 1990

Fig. 3. Relative changes in food/nutrient intake in Japan (1955-1990). Data source: National Nutrition Survey.

18 S. Tominaga. T. Kuroishi/ Cancer Letters 90 (1995) 75-79

intake of selected food and nutrients and breast cancer mortality considering some time-lag be- tween the intake of food/nutrients and death from breast cancer [4]. They confirmed quantitatively the close positive correlation between the intake of fat, dairy products, butter & margarine, oils & fats, meat, cheese and some other animal foods and the breast cancer death rate.

. 3. Geegn#d distribution of breast cancer and related factors in Japan.

The age-adjusted death rates of breast cancer by prefecture in Japan show that mortality is high in Tokyo and other prefectures where metropolitan cities are located. Fig. 4 shows the relative com- parisons of the age-adjusted death rates of breast cancer in five areas according to the population

Age-adjusted incidence mte’

per 100,000 population

RX%! country city/states 0 20 40 60 80 1w

“‘-

USA Hawa I i

Los Angeles

Ch i nese China Tianjln

Shanghai

Hong Kong

SingaDore

USA Hawa I I

Los Ange I es

Indian India Bombay

S i waDore

Whites USA

Fig. 5. Comparison of the incidence rates of breast cancer for selected races and countries in the World. *Standardized on the World population. Data source: Cancer Incidence in Five Con- tinents, Vol. VI (1992) [ll].

size in Japan [4]. A close relation is observed be- tween urbanization and breast cancer mortality. To study the possible risk factors behind urbaniza- tion, Kato et al. compared the intake of selected food and nutrients for the five areas according to the population size and clearly demonstrated that the intake of butter, margarine, ham, sausage and fat was higher in urban areas than in non-urban areas [4]. Kato et al. further examined the correla- tion between the food/nutrient intake and breast cancer death rate among 12 geographical districts in Japan and confirmed the close positive relations between the intake of butter, margarine, cheese, ham, sausage, bread, dairy products, animal pro- tein and fat and breast cancer mortality [4]. Some other factors such as age at marriage, age of the mother at the delivery of her first child and the number of children, etc. may be related to urban- ization.

4. Recent results of migrant study of breast cancer

From many migrant studies [S-lo] the influence of some environmental factors has been im- plicated. Fig. 5 shows the age adjusted incidence rates of breast cancer for selected countries and races. The original data were obtained from “Cancer Incidence in Five Continents, Volume VI” [ 111. Japanese, Chinese and Indians living in home countries and other Asian countries show a low rate of breast cancer, whereas Japanese and Chinese living in the United States show a much higher incidence rate, close to those of whites in the United States. These results confirm the influ- ence of some environmental factors, possibly diet, especially high fat intake, on the incidence of breast cancer.

5. Future prediction of breast cancer in Japan

Tsukuma et al. has predicted the future inci- dence of selected sites of cancer in Japan up to the year 2015 by extrapolating the past trends of sex and age-specific incidence for selected sites [ 121. They predicted that the age-adjusted incidence rate of breast cancer will exceed that of stomach cancer in the near future (in around 1995) and the number of breast cancer incidences will also ex-

S. Tominaga, T. Kuroishi/Cancer Letters 90 (1995) 75-79 79

teed that of stomach cancer by 2015. Thus, breast cancer will become a major cancer among females in Japan in the future.

6, Prevmtioo of breast cancer

As breast cancer has been increasing in Japan and is predicted to increase further in the future, preventive measures, especially primary preven- tion of breast cancer, should be taken. For pri- mary prevention of breast cancer it is proposed to avoid high risk factors, especially avoidable risk factors such as excess fat and calorie intake. It is also desirable from a view point of epidemiology and prevention to avoid a high age of the mother at the dehvery of her first child, but this may not necessarily be easy from a socio-economical view point To compensate for the difficulties in pri- mary prevention of breast cancer, secondary pre- vention (breast cancer screening by breast self examination, physical examination by physicians and by mammography) should be promoted.

References

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