Ethnicity and cancer

DEFINITION: For socioeconomic, dietary, lifestyle, environmental, and genetic reasons, cancer affects various population groups differently. This differs from individual causes that may also affect carcinomas' incidence and mortality rates.

Ethnicity: An ethnic group is distinguished by common cultural and frequently racial, 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, the distinguishing features of a particular ethnic group will become blurred. Even the group’s distinctive health profile will be modified by changes in not only the 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 essential role in determining which ethnic group is afflicted by what type of cancer. Therefore, some ethnic differences in health indicators, including cancer markers, appear independent of socioeconomic status.

Making general statements about the importance of particular factors becomes harder when comparing ethnic groups. Many inconsistencies and correlations are complex because race and ethnicity are defined differently. For example, not all cancer-related data distinguish between non-White and White Latinx.

Some generalizations: The leading causes of cancer death for American men include lung, prostate, colorectal, pancreas, and leukemias. For women, lung, breast, colorectal, pancreas, cervix, and ovary cancers are the most common causes of cancer deaths. Asian, Black, and individuals of mixed ethnicities receive fewer cancer diagnoses than White individuals, but Black individuals have the highest death rates from cancer of any ethnic group. Although the cancers most likely to cause death are largely the same among ethnic groups, their rankings differ.

In men, lung and colorectal cancer is common and deadly throughout ethnic groups, but Black men are at an increased risk for prostate cancer. In Asian Americans and Pacific Islanders, liver cancer and gallbladder cancer are more common than in the general population. Black Americans have nearly twice the chance as the general population for developing stomach cancer.

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 are relevant in explaining cancer trends among ethnic groups. Human geography can explain only part of the incidence of cancer. Genetics also plays a role. For example, women of Ashkenazi Jewish heritage have a higher rate of breast and ovarian cancer than the general population. 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. It 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 ethnicity and socioeconomic differences intertwining. Failure to consider this may lead to inappropriate attribution of differences to ethnic and, thus, genetic factors rather than socioeconomic status, which may misdirect healthcare research and funding. The incidence of cancer falls as levels of education and income rise. Groups with a higher proportion of members with lower socioeconomic status, such as Black Americans and Latinx, have fewer financial, educational, and physical resources and are more likely to be uninsured than groups with higher socioeconomic status.

Some statistics: Black Americans

The incidence rates of the two most common forms of cancer, prostate for men and breast for women, vary considerably by ethnicity. Black Americans are more likely to be diagnosed at a later stage, receive less care, and die from these cancers than individuals of other races and ethnicities.

Black 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. However, studies have shown that within comparable strata of education and income, Black Americans over twenty-five have a similar or lower incidence of all cancers combined when compared with White Americans. This implies many of the disparities in cancer incidence associated with ethnicity may be linked to poverty rather than 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. These 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 Black Americans, different ethnic groups in the United States have distinctive cancer patterns. Relative to White individuals, age-adjusted incidence and mortality rates among Hispanics are higher for gallbladder, stomach, and cervical cancer. Indigenous Peoples are more likely to be diagnosed with liver, stomach, kidney, lung, colorectal, and breast cancers than the general population. Japanese Americans have higher rates of stomach and liver cancer. Chinese Americans have higher rates of nasopharyngeal, liver, and stomach cancer. Hawaiians have higher death rates from the 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, variations in incidence rates often reflect differences in tobacco use, dietary habits, infectious exposures, or access to medical care.

However, some of these higher incidence rates 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 helicobacter infection in childhood and a greater consumption of salted and smoked foods but lower consumption of fresh fruits and vegetables. Similarly, ethnic groups with an 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. In contrast, 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. However, this may change with increased participation in outdoor activities and the depletion of the protective ozone layer in the stratosphere.

The future: Cancer research has brought an 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 healthcare. However, for many cancers, risk differentials among various ethnic groups are related to genetic susceptibility. The development of genotyping techniques opens prospects for additional investigations so research can focus on underlying genetic mechanisms to solve the enigmas posed by interethnic variations in cancer incidence and mortality rates.

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