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16. Are there race differences in cancer occurrence?

Differences may be observed between white and nonwhite popula tions in the United States in the occurrence of cancer. These differences vary greatly by site. Negroes are much less likely to develop cancer of the skin than white people but are more likely to develop cancer of the cervix in females or cancer of the prostate in males. The incidence of primary liver cancer seems unusually high among Negroes a phenomenon that has been reported from parts of Africa as well as this country. (Source: Dorn, H. F., and Cutler, S. J., op. cit.)

CANCER INCIDENCE RATES BY RACE, 10 URBAN AREAS, UNITED STATES, 1947

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17. What are some unusual features of cancer mortality among specific groups in the United States of varying origins?

Cancer mortality among the Japanese, Chinese, and Indians living in the United States and Hawaii differs from that for the remainder of the population in several respects.

Japanese here have a relatively high risk of developing stomach cancer, although not so high as the Japanese in Japan. Chinese in this country have high mortality from cancer of the pharynx, a phenomenon that has been observed among Chinese elsewhere. American Indians have a low cancer death rate generally, but Indian women have high mortality for cancer of the liver and cancer of the cervix. (Source: Smith, R. L., "Recorded and Expected Mortality Among the Japanese of the United States and Hawaii, With Special Reference to Cancer," Journal of the National Cancer Institute, vol. 17, pp. 459-473, 1956. Smith, R. L., "Recorded and Expected Mortality Among the Chinese of Hawaii and the United States With Special Reference to Cancer," Journal of the National Cancer Institute, vol. 17, pp. 667-676, 1956. Smith, R. L., "Recorded and Expected Mortality Among the Indians of the United States With Special Reference to Cancer," Journal of the National Cancer Institute, vol. 18, pp. 385-396, 1957.)

CANCER MORTALITY AMONG JAPANESE AND CHINESE IN UNITED STATES AND HAWAII, 1949-52

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300

100 200 300 0 100 200 MORTALITY RELATIVE TO THAT FOR WHITE POPULATION,

Less than 9 deaths

1949-50 (in percent)

18. How does the occurrence of cancer vary with genetic factors?

For most of the international and racial differences in the occurrence of cancer, data are insufficient to conclude what part of such differences is genetic and what part is attributable to environmental factors such as diet and habits.

The genetic influence has been studied adequately in but few human neoplasms. A tendency for cases to appear with above-average frequency in certain families has been noted in cancer of the female breast, large intestine, and stomach. One rare form of cancer of the eye, called retinoblastoma, and two disease precursors, familial multiple polyps of the colon and an extreme sensitivity to sunlight in people with a skin condition called xeroderma pigmentosum, are strikingly inheritable. There is also some genetic association between group A and stomach cancer and between mongolism and one form of acute leukemia.

19. Are there urban-rural differences in the occurrence of cancer?

Comparisons of cancer incidence for urban and rural populations in the United States have been reported for Connecticut, Iowa, and upstate New York. Data for each of these areas show a higher urban incidence for each cancer site group. In Iowa, where there is a definite contrast between urban and rural populations, the excess cancer mortality for urban areas is slightly greater than in Connecticut or upstate New York, where much of the rural population is engaged in nonfarm pursuits.

Urban-rural comparisons for Denmark and for England and Wales are in general very similar to those reported for the United States. This suggests that systematic comparisons of cancer experience in urbanized and nonurbanized countries may produce epidemiological information of great value. (Source: Haenszel, W., Marcus, S.C., and Zimmerer, E. C., "Cancer Morbidity in Urban and Rural Iowa," Public Health Monograph No. 37 (1956). Griswold, M. H., Wilder, C. S., Cutler, S. J., and Pollock, E. S., "Cancer in Connecticut," Connecticut State Department of Health (1955).)

CANCER INCIDENCE RATES IN URBAN AS COMPARED TO RURAL AREAS, IOWA, 1950

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20. Does cancer occurrence vary by income?

In the United States cancer occurrence is highest in the lowest income groups. This is paralleled by data from Denmark and from England and Wales for socioeconomic groups in these countries. In the United States, however, the gradient by income class is stronger than it is in the other two countries. It is greater among males than females and is greater in the nonwhite than in the white population. These findings do not apply to all sites. Thus, the gradient of cancer incidence with income is strong for the stomach and esophagus but nonapparent for the intestines and rectum. Nor is the relationship always in the same direction. The lowest income group had the highest incidence for cancers of the buccal cavity and respiratory system but the lowest for cancer of the breast. (Source: Dorn, H. F., and Cutler, S. J., op. cit.)

21. What cancers are known to arise from special habits or customs?

In southeast Asia cancer of the oral cavity has been noted to arise from betel chewing. In India a similar effect has been observed from the chewing of khaini, a mixture of tobacco and lime. Where cigars are smoked with the lighted end in the mouth, a Kashmiri custom called Chutta, cancer of the oral cavity tends to result. Where cigarettes are smoked a high risk of lung cancer has been observed. Findings by the American Cancer Society indicate that a man who smokes two packages of cigarettes a day has a risk of developing lung cancer 60 times that for a nonsmoker.

Keeping a heating pot next to the skin, a custom called Kangri in Kashmir and Kairo in Japan, leads to cancer of the abdominal skin. Cancers arise around the loin cloth (dhoti) in India because of the custom of excluding this area from bathing. Circumcision, on the other hand, greatly reduces the chances of developing cancer of the penis and there is even a suggestion that it reduces the risk of cancer of the cervix in the spouse. (Source: Hueper, W. C., "Environmental Factors in the Production of Human Cancer." Cancer (edited by R. W. Raven), vol. 1, pp. 404-496 (1957).)

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