prostate cancer scan
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Prostate cancer is 60 per cent more common in African Americans than in Caucasians, and black Americans are twice as likely to die from the disease when they get it. Yet black men are less likely to be included in clinical trials of drugs for the disease - and accidental biases against their biology seem to be partly to blame.

Speaking at a meeting of the American Society for Clinical Oncology in Chicago this month, Susan Halabi, of Duke University, says her team found that only 12 per cent of the participants in phase 3 clinical trials - the type of late stage trial that is most crucial for drug approval - are black men. This is despite black men making up around 15 per cent of the male population in the US.

Social and cultural factors have long been blamed for lower participation in clinical trials by black men, but researchers are beginning to understand that the way prostate cancer trials are conducted may also be biologically biased against black men.

When researchers establish clinical trials, they will decide upon exclusion criteria. These are usually health issues that could skew a trial's findings on any ill effects a novel drug may have. The idea is that, by testing a new treatment in the fittest possible individuals who have a particular condition, the trial has the best chance of detecting any positive effects. Results can then be generalised to the rest of the population.

Biomarker differences

Earlier this year, a study found that two common exclusion criteria are biased against black men. One of these is the amount of serum creatinine in the blood - this is a measure for gauging kidney health. However, black men tend to naturally have higher levels of this, making them more likely to be left out of trials because of this biomarker.

The second is absolute neutrophil count - the number of a type of common white blood cell - a man has. This is used as a rough proxy for how healthy a person's immune system is which is important, because some cancer treatments can impair this. But black men tend naturally to have counts that are around 7 per cent lower than average, due to a condition called Benign Ethnic Neutropenia (BEN).

Marie Vastola, at the Dana-Farber Cancer Institute in Massachusetts, and her colleagues found that nearly half of all prostate cancer trials use at least one of these criteria. They were especially surprised to find that a quarter of trials use serum creatinine, and more than a quarter of these don't adjust their metrics to take into account the differences in biomarkers in black people.

Health barrier

Eight years ago, a study done by National Institutes of Health came to a similar conclusion about neutrophil counts, stating that automatically excluding people because of BEN is not medically justified and can reduce minority participation in cancer trials. Vastola and her colleagues' findings suggest that this finding has largely been overlooked since then.

The problem goes beyond biomarkers. Halabi's team have also found that the health of black men can also bar them from equal access to clinical trials. High blood pressure, blood sugar, and cholesterol are all traits that are more common in black men. Clinical trials will often use these to refine their participants to healthier people, again favouring white participants over black. If these parameters were loosened, it's possible more people would die during trials, and it would become harder to get a clear picture of a drug's efficacy or otherwise.

"It's a fine line," says Sumanta Kumar Pal, an oncologist at the City of Hope Medical Centre in California. "We don't want to make eligibility so relaxed that we put patients in danger when they enter into clinical trials."

Yet until prostate cancer drugs are tested in groups that are representative of the population, their findings cannot be generalised to anyone other than the predominantly white men participating in them. "I think we need to sit down and re-examine some of these exclusion criteria," says Halabi.