What is the relationship between ethnicity and cancer?
Ethnicity: An ethnic group is distinguished by common cultural and frequently racial or linguistic, social, or religious characteristics. When there is prolonged mingling of ethnic groups within a geographic area or when an ethnic group is exposed to a new environment, as in the case of immigrants to the United States, the distinguishing features of a particular ethnic group will become blurred. Even the group’s distinctive health profile will be modified by virtue of changes in not only environment but also income, educational level, and thus diet, lifestyle, and access to medical care—in short, socioeconomic status. Although socioeconomic status, which varies among different ethnicities, has considerable bearing on the incidence of cancer, inherited predispositions also play an important role in determining which ethnic group is afflicted by what type of cancer. Therefore, some ethnic differences in health indicators, including cancer markers, appear to be independent of socioeconomic status.
Making general statements about the importance of particular factors becomes harder when comparing different ethnic groups. Although some minority older adults, particularly blacks and generally American Indians and Alaska Natives, are considerably less healthy than older whites, others, particularly Hispanics and Asian Americans and Pacific Islanders (AAPIs), are often healthier. There are many inconsistencies, and correlations are difficult, to begin with because the terms race and ethnicity are variously defined. For example, not all cancer-related data distinguish between nonwhite Hispanics and Latinos and white Hispanics and Latinos. Despite these caveats, a few correlations can be hypothesized.
Some generalizations: According to the Centers for Disease Control and Prevention, the five leading causes of cancer death for American men in 2011, expressed as age-adjusted death rates per 100,000 people, were lung, 57.9; prostate, 20.8; colon and rectum, 18.1; pancreas, 12.5; and leukemias, 9.3. The five leading causes of cancer death for American women in 2011 were lung, 37; breast, 21.5; colon and rectum, 12.8; pancreas, 9.5; and ovary, 7.5. Although the cancers most likely to cause death remained largely the same among ethnic groups, their rankings differed. In men, lung and colorectal cancer retained their rankings (one and three) throughout the ethnic groups, but in Asian Americans and Pacific Islanders, liver cancer replaced prostate cancer as the number-two cause of mortality. While the overall male rate for stomach cancer 4.4, for African Americans it was 8.8. In women, lung cancer was the number-one cause of mortality except for Hispanics, in whom the first- and second-ranked causes of death were reversed. Colorectal cancer was the third cause of death in all female ethnic groups. Pancreatic cancer was the fourth cause of death among female American Indians and Alaska Natives.
For all forms of cancer in 2011, the incidence and mortality rates per 100,000 population broken down by ethnic categories were as follows: whites, 449.7 and 168.5, respectively; blacks, 458.3 and 199.2; Hispanics, 350.6 and 117.9; Asian Americans and Pacific Islanders, 290.4 and 105.5, and American Indians and Alaska Natives, 273.4 and 111.5.
Cancer and the role of ethnicity: Worldwide, there are regional variations in the incidence of specific types of cancer according to the ethnicities predominant in those areas. The stomach cancer common in Japan and Scandinavia is thought to be of dietary origin, while the liver cancer common in parts of Africa and Asia is believed to be a result of infection with the hepatitis B virus. However, when people from these areas immigrate to the United States, they often acquire the health profile of Americans through consuming more red meat and living a more sedentary lifestyle. For example, Chinese Americans, who no longer follow the fish, rice, and vegetable diet and active lifestyle of their ancestors, tend to have a higher rate of colorectal cancer as a result.
Nature and nurture both appear to be relevant in explaining cancer trends among different ethnic groups. Factors in human geography can explain only part of the incidence of cancer; genetics also plays a role. For example, Ashkenazi women have a higher rate of breast and often ovarian cancer than women in the population at large. Although rare in the general population, the A636P mutation is detected in up to 7 percent of Ashkenazi Jews with early-age-of-onset colorectal cancer and may account for up to one-third of hereditary nonpolyposis colorectal cancer (HNPCC) in the Ashkenazi Jewish population.
The difficulty of linking ethnicity to hereditary cancers stems from the fact that ethnicity and socioeconomic differences are intertwined. Failure to consider this may lead to inappropriate attribution of differences to ethnic and thus genetic factors rather than to socioeconomic status, which in turn may misdirect health care research and funding. The incidence of cancer falls as levels of education and income rise. Ethnic groups with a higher proportion of members with lower socioeconomic status, such as African Americans and Hispanics, tend to be less knowledgeable about health matters, have fewer financial resources to devote to them, and be more likely to be uninsured than groups with higher socioeconomic status.
Some statistics: African Americans
The incidence rates of the two most common forms of cancer, prostate for men and breast for women, vary considerably by ethnicity. African Americans, with an incidence rate of 194.7 per 100,000 people, had the highest rate of prostate cancer, followed by whites, with a rate of 128.3 per 100,000. However, the incidence rate of breast cancer was higher in white women, with 122.8 per 100,000 versus 121.2 per 100,000 for black women.
In 2011, in men the incidence of all invasive cancers combined per 100,000 people was 554.5 among African Americans, 499.7 among whites, 393.5 among Hispanics, 293.5 among American Indians and Alaska Natives, and 310.1 among Asian Americans and Pacific Islanders. In women, the incidence rates were 393.8 among African Americans, 414.8 for whites, 261.0 for American Indians and Alaska Natives, 324.2 for Hispanics, and 279.8 for Asian Americans and Pacific Islanders.
African Americans experience disproportionately high age-adjusted cancer incidence and mortality rates, but few studies have separated the impact of lower socioeconomic status from that of genetics. In 2011, the cancer death rate for African Americans was 199.2 per 100,000 people versus 168.5 per 100,000 for white Americans. However, studies have shown that within comparable strata of education and income, African Americans aged twenty-five and over have a similar or lower incidence of all cancers combined when compared with white Americans. This implies that many of the disparities in cancer incidence associated with ethnicity may be caused by factors linked to poverty rather than to genetics. Lower socioeconomic status limits educational attainment, reduces access to medical screening or care, and is often associated with greater exposure to tobacco use, heavy alcohol consumption, poor nutrition, physical inactivity, overweight and obesity, and other risk factors. Nevertheless, exactly why cancer incidence and death rates are higher in African American men is not completely known, although mortality rates may be influenced by the tendency for cancer to be diagnosed at a later stage among people with lower socioeconomic status, which results in poorer survival rates.
Other ethnic groups: Besides African Americans, other ethnic groups in the United States have distinctive cancer patterns. Relative to whites, age-adjusted incidence and mortality rates among Hispanics are higher for gallbladder, stomach, and cervical cancer. American Indian men and women have lower incidence rates of most cancers other than those of the gallbladder and stomach. Japanese Americans have higher rates of stomach and liver cancer. Chinese Americans have higher rates of nasopharyngeal, liver, and stomach cancer. Native Hawaiians have higher death rates from esophagus, liver, pancreas, lung, breast, and cervical cancer. Filipinos have a lower risk of most cancers other than those of the stomach, liver, oral cavity, and esophagus. Again, many of these ethnic differences are believed to reflect differences in tobacco use, dietary habits, infectious exposures, or access to medical care.
Some of these higher incidence rates, however, can be attributed to specific causes. For example, the high rate of stomach cancer among recent migrants from Latin America, Asia, and parts of Africa correlates with a higher prevalence of chronic helicobacterial infection in childhood and a greater consumption of salted and smoked foods but lower consumption of fresh fruits and vegetables. Similarly, ethnic groups with increased incidence of liver cancer usually have a higher prevalence of infection with the hepatitis B virus or less commonly hepatitis C virus. The incidence of cervical cancer may reflect exposure to human papillomavirus (HPV), especially when sexual activity begins early and with multiple partners, as is the case with some ethnic groups, whereas the survival rate from cervical cancer varies according to the use of Pap tests and early treatment. In some ethnicities, darker skin, with its increased pigmentation and melanosomal dispersion, helps protect people from skin tumors, but this may change with increased participation in outdoor activities and the depletion of the protective ozone layer in the stratosphere.
The future: Research into cancer has brought increased understanding of the major environmental determinants of cancer, such as infections, diet, tobacco, and exposure to ultraviolet (UV) rays and certain chemicals. Differential exposure to these risks explains to a considerable degree why ethnic groups have varying rates of cancer, especially as, because of socioeconomic status and culture, they differ in levels of early screening, diagnosis, and access to health care. However, it appears that, for many cancers, an important component of risk differentials among various ethnic groups is related to genetic susceptibility. The development of genotyping techniques opens prospects for additional investigations, so that research can focus on possible underlying genetic mechanisms to solve the enigmas still being posed by interethnic variations in cancer incidence and mortality rates.
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