Azara Blog: Prostate cancer test has been woefully wrong for obese men

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Date published: 2007/11/24

The BBC says:

Doctors must take body weight into account when reading test results for prostate cancer as obesity may distort the findings, a US study argues.

Obese men have more blood so the concentration of antigen, a marker for the disease, is lower, a team found.

The North Carolina study, published in the Journal of the American Medical Association, involved 14,000 patients.

It may explain why obese men seem to have more aggressive cancers, as tumours may initially be missed.

The test for prostate-specific antigen, or PSA, is known to be notoriously unreliable.

About a third of men with raised PSA levels will not have cancer, and will undergo unnecessary invasive tests.

Meanwhile, the test sometimes misses prostate cancer, as highlighted in this study.

"We've known for a while that obese men tend to have lower PSA scores than normal weight men, but our study really proposes a reason why this happens, and points to a need for an adjustment in the way we interpret PSA scores to take body weight into account," said Dr Stephen Freedland, a urologist at the Duke Prostate Center.

"If not, we may be missing a large number of cancers each year."

At the extreme, the men in the most obese category had PSA concentrations as much as 21% lower than those of normal weight men.

Dr Chris Hiley, of the Prostate Cancer Charity, said: "This study shows us yet another downside to obesity. An obese man's true PSA level is diluted by his increased blood volume caused by excess weight.

"Doctors now need to work out how to take this into account so they can make an accurate estimate of the PSA level - important in the diagnosis and management of prostate cancer."

Unbelievable, a health study that actually seems to have done some good and found a real effect. But the remarks of Hiley are bizarre beyond belief: "This study shows us yet another downside to obesity". No, this study shows that doctors have been using an incorrect diagnosis for obese men. If for some reason doctors had originally used obese (which these days is pretty much the same as "normal") men instead of "ideal" or underweight men to calibrate the tests then we would now be finding that the latter were the men with the incorrect diagnosis. And would Hiley then be claiming: "This study shows us yet another downside to not being obese"? Of course not.

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