Harvard Reports on Cancer Prevention
Volume I: Human Causes of Cancer
Cancer Causes & Control:
An International Journal of Studies of Cancer in Human Populations
Official Journal of the International Association of Cancer Registries
Volume 7 Supplement November 1996 ISSN 0957-5243

Socioeconomic Status

Introduction
A British obstetrician remarked in 1902 that carcinoma of the cervix was a disease occurring "almost exclusively among the poor, the chronically overworked and underfed, among women, poor, prolific, harassed, worried...reposeless."¹ Since that time, numerous reports from different countries have confirmed that economically disadvantaged groups in society are at increased risk of cancer.

Among individual types of cancer associated most consistently with low socioeconomic status (SES) are cancers of the lung, cervix, and stomach.² Many studies also have reported higher rates among the poor for cancers of the esophagus, oral cavity, larynx, liver, and bladder.^3-7 Sufficient evidence had accumulated on low SES and increased cancer risk for the director of the United States National Cancer Institute (NCI) to declare in 1991 that "poverty is a carcinogen."⁸ The total cancer incidence attributable to poverty (family income of less than $15,000) is 16.5 percent for Whites and 12.1 percent for Blacks.

Social environment
To a considerable extent, socioeconomic disparities in cancer risk are explained by known contributions of personal health habits, such as higher cigarette smoking, excess alcohol intake, or poor diet among lower SES groups. For example, the gradient in lung cancer risk across income groups in Figure 1 (from the study by Bacquet et al⁶) most likely reflects patterns of cigarette consumption across social class. On the other hand, disparities in lung cancer mortality across social class have been shown to persist even within nonsmokers.^5,7 Therefore, if something is to be done about reducing socioeconomic disparities in cancer, we must look beyond the explanation that such differences result from the health habits of the poor. This is because socioeconomic differences in health arise not just as a consequence of personal choice, but also because of constraints posed by the social environment in which people lead their lives.

Advertising campaigns by the tobacco industry have been shown to target selectively lower SES groups.⁹ Giving up smoking to avoid cancer may have lower priority for some people living in poverty, compared with the stresses that they must confront on an almost daily basis.¹⁰ Families residing in low-income neighborhoods frequently are restr icted in their dietary choices by the lack of availability of retail stores purveying healthy foods, and an overabundance of liquor stores and junk food outlets (a business practice sometimes referred to as red lining).¹¹ Thus, reducing the socioeconomic burden of cancer is unlikely to be achieved by simple admonishments to poor people to avoid imprudent health habits. Even a person's work, which defines one's social position, is a powerful determinant of exposures to occupational carcinogens over which individuals can exercise less personal control than decisions such as to quit smoking. Animal data on the transgenerational transmission of carcinogenic risks suggest that parental occupational exposure before conception may increase the risk of cancer in the progeny,¹² just as socioeconomic disadvantage can be passed on to future generations.

Incidence, survival, and access
If poverty is not always associated with increased incidence of cancer, it has been shown repeatedly to be related to poorer survival following the onset of cancer. For example, affluent women have a higher incidence of breast cancer (6), yet they have better survival from the disease compared with socioeconomically disadvantaged women.¹³ There are several reasons why poorer people experience worse cancer survival. In the case of breast and cervical cancer, lower SES women present for medical treatment with more advanced disease than more affluent women.¹⁴ The survival advantage of upper SES women may reflect, in part, earlier diagnosis. Nonetheless, according to the 1990 US National Health Interview Survey (NHIS), women with annual incomes greater than $46,500 were twice as likely to have received a Pap smear within the past two years, and nearly three times as likely to have undergone a mammogram within the previous year compared with the poorest women (annual income less than $15,200).¹⁵ Poor people may have less opportunity to seek preventive care because of the competing demands of employment or child rearing as well as difficulties in arranging transportation.

Even after the diagnosis of cancer has been made, people in lower socioeconomic groups may receive differential treatment from healthcare providers. A study of over 1,800 lung cancer patients treated in northern New England hospitals¹⁶ found that more educated as well as privately insured patients received more aggressive therapy. This differential treatment is compounded further by lack of continuity in healthcare. People of lower SES tend to depend on emergency room care because they are underinsured or uninsured.¹⁷

While lack of access to healthcare presents a major barrier toward reducing the SES gap in cancer survival, it should be noted at the same time that similar disparities have been found in countries with universal access to medical care.^16,18 Moreover, differences in survival have been documented for cancers with poor prognosis (e.g., lung and pancreas), where presumably access to treatment has little influence on outcome.¹⁸ Even in a country such as the US, with documented inequality in access to preventive medical care, the bulk of SES disparities in cancer screening occur among women who already have access to health insurance.¹⁵ Thus the search for the elimination of social disparities in cancer survival must go beyond the provision of adequate and timely medical care.

One potentially important difference between SES groups is in their exposure to psychosocial stress as well as the amount and availability of their coping resources. Lower SES groups lack the level of social networks and supports reported by higher SES groups. The reasons for this, among many, include loss of social connections caused by unemployment, marital dissolution brought on by economic instability, and depletion of social resources within disadvantaged communities.¹⁹ It has been suggested²⁰ that stronger social networks are associated with lower cancer mortality, while provision of social support to cancer patients may increase their chances of survival.²¹ If social support actually does improve cancer survival, then the mechanisms have not been clearly established. These may consist of a combination of instrumental support (money, labor in kind), informational support (resulting in better compliance with treatment), and emotional support.

Although race has been used frequently as a proxy for socioeconomic status in the US, this practice should be discontinued, as it is imprecise and potentially misleading. While it is true that African-Americans are over-represented among the poor, two-thirds of the 34 million Americans currently living in poverty are, in fact, White.²² In the study by Baquet et al⁶ based on SEER cancer incidence data, Blacks had seven to 10 percent higher age-adjusted incidence rates for all cancer sites compared with Whites. However, when the data were adjusted for socioeconomic status (income and education), the overall cancer incidence rate for Blacks was seven percent lower than for Whites (see Figure 1). There is no question that Blacks suffer from higher age-adjusted mortality rates than Whites for cancers of the lung, breast, colon, prostate, cervix, stomach, larynx, and pancreas²³ and that these trends call for urgent action. Nevertheless, the variable 'race' has a different conceptual meaning from socioeconomic status, and its contribution to cancer risk should be addressed in its own right.

Conclusion
Socioeconomic disparities in cancer are large, persistent, and possibly widening.¹² The solution to reduce such disparities must take many forms: from action at the broadest level of society—such as social policies designed to alleviate both absolute and relative deprivation—to interventions at the level of communities—such as campaigns to remove cigarette vending machines and billboards—that help deprived neighborhoods overcome cancer. Twenty-five years after President Richard Nixon declared war on cancer, it is increasingly evident that fighting cancer also requires war on poverty.²⁴

Summary Points

Suggested Further Reading

References