Cancer Across Cultures
Epidemiologists track gender, race and ethnicity to better understand the factors affecting cancer risk.
When
cigarettes grew popular during the late 19th and early 20th centuries, many
touted them as healthy. Yet, with the increase in smoking, lung cancer—one
of the rarest cancers in 1900—rose to the top of the list of most common
cancers in the Western world by 1970.
Not until scientists observed decades of rising lung cancer rates did the public truly get the message about the health risks associated with smoking.
Today’s changing trends in cancer may be less dramatic, but they still give epidemiologists hints about how diet, exercise and lifestyle influence cancer risk and whether public-health measures are working.
To better understand the factors affecting cancer risk—and how cancer impacts society—researchers in California compile information about every cancer diagnosis and cancer-related death in the state. And by tracking the gender and ethnicity of each case, researchers may better understand how cancer impacts different parts of the population.
Among Californians, for example, black men are five times more likely to die of cancer than are South Asian men. Yet rates of certain cancers, such as liver and stomach cancer, are much higher among some Asians than among blacks.
That is just one intriguing piece of information found by researchers with the Los Angeles Cancer Surveillance Program, or CSP, which recently analyzed 14 years of data from the California Cancer Registry to create the most thorough report ever on cancer trends statewide. The CSP is based at USC/Norris Comprehensive Cancer Center.
“Identifying differences and trends in cancer rates by race and ethnicity is the key to identifying how successful our cancer control efforts are, and tells us a lot about the causes of cancer, and how to prevent it,” says Myles Cockburn, Ph.D., assistant professor of preventive medicine at the Keck School of Medicine of USC and co-lead author of the report.
The report, “Cancer Incidence and Mortality in California: Trends by Race and Ethnicity 1988-2001,” shows the number of yearly cancer cases per every 100,000 people, a ratio called an incidence rate. It also shows the same ratio for deaths from cancer, called a mortality rate.
Researchers examined 24 types of cancer to see how rates changed over time. These types, below, are but a few of the cancers covered.
Melanoma
One of the body’s most visible cancers is also one of its most deadly.
Melanoma accounts for three quarters of all deaths from skin cancer—about 7,900 American lives every year. Yet it only comprises a small proportion—4 percent—of all skin cancer cases. Its lethal nature underscores the dire need for more screenings and preventive strategies.
Whites in Australia, New Zealand and California have the world’s highest melanoma rates, and the problem is worsening: Melanoma was the fastest-increasing cancer among whites worldwide over the past two decades.
And among white Californians, rates have risen so quickly that melanoma is now among the five most common cancers.
“While some of these increases may be due to increased screening activities, it is most likely that they reflect an important increase in risk for the disease, particularly from sun exposure,” says Cockburn. “Much of the increase in invasive cancers occurred among large tumors, rather than small ones that tend to be found with screening. People born in the 1960s who got a lot of sun exposure during their childhood have been reaching the age when melanomas arise.”
Screening’s importance also can be seen through the rapidly increasing rates of localized, or in situ, melanomas in whites.
“In situ melanomas have not had a chance to spread to nearby tissue, often because they are uncovered at an early stage, due to screening,” Cockburn says. “And among whites, they more than doubled during this time.” That may be good news, in part, because in situ melanomas are considered highly curable.
But the story is different among Latinos. Though melanoma is rare in this group, invasive melanoma rates increased slightly among men and remained steady among women from 1988 to 2001. “This is an important trend, because most melanoma and skin cancer prevention programs are aimed at non-Latino white populations, not at Latinos,” Cockburn says.
During this time, in situ melanomas remained steady in Latino men and increased among Latinas. Researchers suggest that screening efforts may have reached whites most effectively, and may possibly have reached Latinas, but more work may need to be done to reach Latino men.
Breast cancer
Breast cancer is the most common cancer among all women in California, no matter their ethnicity, and the disease has been growing among some groups in particular.
White women are hardest hit by breast cancer, and rates for new breast cancer cases rose steadily among these women between 1988 and 2001 in California. By the beginning of the 21st century, about 150 white women in every 100,000 each year were diagnosed with the cancer.
Black women also continue to have high breast cancer rates—about 120 new cases in every 100,000 women each year—although rates have remained consistent since 1988. Latinas, too, have had stable breast cancer rates, typically half those of white women.
“We are seeing the largest changes in Asian populations, though,” says Dennis Deapen, Dr.P.H., executive director of the Cancer Surveillance Program, professor of medicine at the Keck School and co-lead author of the CSP report.
Asian women have traditionally had low breast cancer rates. Korean women, for example, are less than a third as likely to be diagnosed with breast cancer than are white women, but their rates are rapidly rising. Invasive breast cancer cases have grown significantly among Japanese and Chinese women, and especially among South Asians and Koreans.
Researchers suspect that Asians’ breast cancer rates have risen as immigrant women have adopted elements of a Western lifestyle, especially having fewer children and delaying having children until later in life.
At the same time, statistics show that mammography may be saving lives. While breast cancer incidence rates have risen, mortality rates for most women have dropped or stayed about the same.
“Rates for in situ breast cancers have doubled or even tripled for some groups during this time, as well. These are breast cancers that are more often found by screening,” Deapen says. “Although we can’t say for certain that this is due to mammography, it is likely that improving early detection may have contributed to the discovery of these cancers and of early stage malignant disease.”
Prostate cancer
As the nation’s population ages, researchers are racing to add to medicine’s knowledge about prostate cancer, primarily a disease of the elderly.
No one knows exactly what causes prostate cancer, but researchers have some ideas.
Rates vary widely around the world, with Americans and Canadians having the world’s highest rates of the disease. When immigrants from nations with low prostate cancer rates move to other nations with high rates, their prostate cancer rates begin to rise.
“This hints that although there are strong hormonal and genetic factors involved, prostate cancer risk may be related to lifestyle factors, such as diet, tobacco use, activity levels, obesity, and possibly alcohol use and reproductive or sexual issues,” Cockburn says.
Prostate cancer is the most common cancer among all Californian men except Koreans and Vietnamese.
Black men have, by far, the highest prostate cancer rates of any group in the state, followed by whites and Latinos. Koreans have the lowest rates, and are about an eighth as likely as black men to be diagnosed with prostate cancer.
Rates for most groups in California spiked in the early 1990s, probably because doctors were increasingly testing for prostate-specific antigen, or PSA, as a marker for prostate cancer. Prostate cancer incidence dropped back to previous levels for most men in the mid-1990s.
Filipinos, South Asians and Vietnamese actually saw their rates increase in the mid-1990s, then drop or level out in the late 1990s. Researchers suspect these men did not access PSA testing as quickly as more established groups. Among Chinese, meanwhile, prostate cancer rates have steadily increased since 1988.
During the same time, prostate cancer mortality rates have been dropping among all groups. Researchers say that improved treatments may be making a difference, since most of the reduction in deaths has come from men with advanced disease.
“Scientists are aggressively looking at the factors that increase risk for prostate cancer,” Cockburn says, “and as time goes on, we hope that prevention efforts focusing on these factors can make a real impact on public health.”
Esophageal cancer
In California and across the nation, blacks traditionally have had the highest rates of esophageal cancer. When researchers look closer at the statistics, though, they see big changes underway.
After the late 1980s, new cases of esophageal cancer among blacks in California began to plunge. At the same time, new esophageal cancer cases among whites began to creep upward. By 2001, esophageal cancer became almost as common among whites as it was among blacks.
Rates also fell rapidly for Chinese men and slightly for Latino men.
“These rates actually reflect changing trends in different kinds of esophageal cancers,” says Cockburn. “And these changing trends hint at different risk factors that may be behind the cancers.”
There are two main kinds of esophageal cancer, physicians explain: squamous cell carcinoma and adenocarcinoma.
Squamous cell carcinoma can occur anywhere in the esophagus. Smoking and alcohol consumption are the main risk factors behind this type, which, at one time, accounted for about 90 percent of esophageal cancers.
Adenocarcinoma, meanwhile, grows from abnormal glandular tissue, usually in the lower part of the esophagus. This tissue can grow there abnormally because of gastroesophageal reflux disease, a condition in which stomach acid escapes into the esophagus.
Today, about two-thirds of esophageal cancers are adenocarcinomas.
“Most of the increase we saw in esophageal cancer among white men in California could be attributed to an increase in adenocarcinoma,” Cockburn says.
Adenocarcinoma is rare among blacks, he adds.
In the future, researchers hope to better understand the differences in causes behind the two esophageal cancer types and improve early detection measures.
Colorectal cancer
In some ways, cancers of the colon and rectum are a disease of Western culture. Sedentary lifestyles and the high-fat diets of today’s fast-food society probably add up to increased colorectal cancer risk, while regular exercise combined with a more basic diet heavy in vegetables and fiber seem protective.
Colorectal cancer is most common in the United States, Canada, northern and western Europe, Australia and New Zealand, and is rarer in Asian countries. But when people from countries of low colorectal cancer risk immigrate to countries of high risk, their chances of developing the disease appear to rise, reflecting how important diet and lifestyle can be for cancer risk.
Statistics from California bear that out.
Although blacks and whites in California have the highest rates of colorectal cancer, and rates among most Asians are low, colorectal cancer has been on the rise since 1988 in three groups: Korean men and women, South Asian women and Filipino women. The rate of deaths from colorectal cancer among Korean women has been increasing as well.
Researchers believe that the increasing colorectal cancer rates among Koreans, who traditionally have had a low risk of colorectal cancer, probably result from rapid acculturation—especially the adoption of high-fat diets—in this group, even compared to other migrant populations.
Californians of Japanese descent have the third highest colorectal cancer rates, behind whites and blacks; researchers say that is likely because Japanese immigrated to the state and adopted a Western lifestyle earlier than most other Asian groups.
Colorectal cancer rates also can shine light on the effectiveness of regular screening, such as the use of sigmoidoscopy and colonoscopy. These routine tests can mean a better chance of finding colorectal cancer at an early stage, when it is most curable. Screening even allows physicians to discover and remove colon polyps before they turn cancerous.
“Between 1988 and 2001, the incidence of colorectal cancer declined among whites and blacks in the state,” Cockburn says. “The rates for death from this cancer also went down among white and Japanese men and women and among black women. This can likely be linked to the effect of screening.”
Some groups have apparently benefited from screenings more than others: Researchers have shown that Koreans and Filipinos in California are especially underscreened.
Although rates of colorectal cancer are considered low among Asian groups in California, the cancer still ranks as either the second or third most-common type for all groups except Vietnamese men, in whom it is the fourth most-common cancer.
Clearly, say researchers, improving education, prevention and detection of all cancers among all groups could greatly impact public health.
“Cancer Incidence and Mortality in California: Trends by Race/Ethnicity 1988-2001” may be downloaded at www.ccrcal.org/PDF/CCRmonograph12-04.pdf.
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