Race, genes, and cancer.

Science, technology, and life.
July 14 2009 7:28 AM

Mortal Skin

Race, genes, and cancer.

Black people, on average, are more likely to die of cancer than white people. Is part of that difference genetic?

The Journal of the National Cancer Institute just published a big study on this question. If you haven't heard about the study, maybe that's because you get your news from television, National Public Radio, the Associated Press, or the New York Times, which have ignored it. Why would they ignore it? Because the study suggests the answer is yes. It's OK to report that racial differences in cancer outcomes are caused by poverty and discrimination. It's not OK to report that they're inherited.

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

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The study, which tracked nearly 20,000 patients in a series of clinical trials, painstakingly accounted for environmental factors. It concluded that "African American patients with breast, prostate, or ovarian cancer … had statistically significantly worse overall survival than white patients," even though "all patients had uniform therapy and follow-up parameters, with adjustment for stage, socioeconomic factors, and known prognostic variables."

The authors reported "an increase in mortality … among African American women with ovarian cancer in our population who were treated uniformly on phase III clinical trials after adjustment for all available factors."  A similar "disparity in survival was even observed in equal access care systems, such as Kaiser Permanente." Consistent with previous studies, "the disparity in prostate cancer survival persisted despite adjusting for income and education." In fact, in one previous study, "African American race was the only independent predictor of time to prostate-specific antigen progression, indicating that biological and genetic differences underlie this disparity."

In a search of Nexis, I can find only two American reporters who covered the study: Deborah Shelton of the Chicago Tribune and Rob Stein of the Washington Post. Stein reports:

Because all the cancers for which the disparity persisted were related to gender, the findings suggest that the survival gap may be the result of a complex interaction of differences in the biology of the tumors and inherited variations in genes that control metabolism of drugs and hormones, [Kathy Albain, the study's lead author] said. … "This is almost certainly related to a mix of factors across races pertaining to tumor biology and inherited factors," Albain said. … "What we are saying is that there is something that 'tracks' with African ancestry only in these three diseases."

In both articles, critics reject the study's findings or belittle them as a distraction from the real causes of racial differences in cancer outcomes. Steve Whitman, director of Chicago's Sinai Urban Health Institute, tells Shelton that the study failed to account for "residual social variables." He dismisses it as a rehash of the old notion that "the problem is not with society, not with social issues, it's not with racism, but with the biology that lies within black people." Otis Brawley, the American Cancer Society's chief medical officer, tells Stein, "When I hear scientists talking about racial differences, I worry that it starts to harken back to arguments about genetic inferiority." He insists that the gaps in cancer outcomes "are not due to inherent genetics. They are due to the effects of environmental factors like diet and exercise and obesity on biology."

I've heard vehement denials like these before. Two years ago, I wrote about the possible role of heredity in racial gaps on IQ tests. That earned me a wave of denunciation unlike anything I'd ever experienced. Some of the criticism was deserved, but much of it was an overreaction based on fear and misunderstanding. People are afraid that if we acknowledge genetic differences along racial lines, we'll become blind to discrimination and socioeconomic inequality, and we'll lay a scientific foundation for segregation. That isn't true.

Race is enormously complicated. As a scientific category, it's useful but crude. It sorts people not into separate groups but into overlapping clouds, defying predictions about individuals. It correlates to some extent with culture and economics but also to some extent with genes. Denying that race is real or that genes play a role in racial differences is just as simplistic as pretending that race explains everything or that discrimination has vanished.

If you really want to understand the relationship between race and cancer, don't read Brawley's comments to the Post. Read his nuanced editorial in the journal that published the study. He makes several important points. First, he notes that the study matches previous data:

Albain et al. found that black race was associated with increased mortality in patients with breast, ovarian, and prostate cancers, despite uniform stage, treatment, and follow-up. These results largely agree with the results of an analysis of clinical trials by Bach et al. in 2002, and it is noteworthy that the only racial differences in treatment outcome are from sex-related tumors.

Second, he points out that the racial discrepancies aren't binary. They're diffuse patterns in which groups overlap, though their averages differ:

In the United States, we frequently do a sort of racial medical profiling. We accept that our racial labels predict for groups of people less likely to do well with cancer and other diseases. … Taken together, the two studies and others do not suggest that blacks have a different kind of breast cancer but rather that there are multiple kinds of breast cancer and that a higher proportion of black patients with breast cancer have the worse kinds. No race has a monopoly on the good kind, nor the bad kind of breast cancer, but the prevalences differ.

Third, he explains that race is a rough, transitional category:

It is more scientific to think of race as a surrogate for area of geographic origin, socioeconomic status (SES), and culture, all of which can have correlations with disease risk. Area of geographic origin is a legitimate scientific categorization. There are genetic markers that have a higher prevalence in some populations as defined geographically. For example, the sickle cell mutation is found in sub-Saharan and North Africa, the Middle East, and the Mediterranean countries of Europe. Furthermore, pharmacogenetic studies demonstrate that certain drugs are less likely to work or more likely to cause side effects in populations from certain areas ...

Fourth, he reminds us that environmental factors contribute to unequal cancer outcomes:

A substantial body of work demonstrates that black-white disparities in most cancers are due to the fact that a large proportion of minority and poor patients receive less than optimal care when compared with nonminority patients. Studies suggest that for most cancers, equal treatment yields equal outcome among equal patients and there is not equal treatment.

Taken together, these points form the beginning of a sensible way to think about race. It's a fluid category. It can be economic, cultural, and genetic. It can be salient but also coarse. Analytically, it's a primitive tool. Can it tell us useful things? Yes. Should we use it? Yes, but judiciously. In the case of cognitive ability, it probably does more harm than good. But in the case of drug reactions or cancer, lives are at stake.

Our responsibility is to use this tool wisely and, at the same time, begin to replace it with more sophisticated models of interacting dynamics—economics, culture, genetics—that more accurately fit the data. If we succeed, tomorrow's doctors won't have to guess your prognosis from your race. They'll have your genome and plenty of other biological information about you, much of it inherited. And they won't have to pretend it doesn't matter.

(Now playing at the Human Nature blog: 1) BlackBerries are black holes. 2) How to help machines avoid killing people. 3) Saving dogs from diseases we inflicted on them.)