Obesity 'may distort cancer test'

[Demi]

BBC News Online
London, UK
24 November, 2007


Obesity 'may distort cancer test'

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."

Working it out

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."

She added: "This finding could also be of wider significance in interpreting blood tests in other conditions that affect both men and women."

In the UK, the disease now accounts for 13% of male cancer deaths, and is the second most common cause of cancer death in men, after lung cancer.


http://news.bbc.co.uk/1/hi/health/7104075.stm

[I_have_PCa]

The test for prostate-specific antigen, or PSA, is known to be notoriously unreliable. I just HAVE to take exception to this statement. It is ONLY unreliable when used by doctors who are not current on the developments in Prostate Cancer. That is, just like ANY other test, you must CORRECTLY interpret the results. It is not a binary test, that is, positive or negative, like is the light switch on or off?

PSA is directly related to the amount of prostate tissue that is producing the antigen. And for those that do not know this, very advanced prostate cancer cells are SO far from the normal healthy state that they do not produce any PSA, they just reproduce and reproduce. This is a STRONG reason to get a YEARLY PSA test so your cancer does not get this far advanced before you find it. That is almost what happened to the man at work.

Many men can have benign hyperplasia, enlarging of the prostate, which is not cancerous. My neighbor is a case in point. His PSA was 7 to 9, up and down. The Urologist wanted to do a biopsy,since he only knew that over 4 was the point at which PCa should be suspect, not knowing about hyperplasia, apparently. I got him good information which he used to go to a specialist (top of this area of the field) who assured him that he did NOT have PCa.

So how do the experts in the field use PSA? They now also use the rate of increase in PSA, expressed in the time for the PSA to double, as well as the absolute value. They have given this parameter the appropriate name PSA Velocity. The aggressiveness of the cancer is now being rated by the range of the PSA Velocity. The breaks, if I remember right, are 3 months and one year. Under 3 months being VERY aggressive, requiring IMMEDIATE treatment, usually hormone blockade to shut off the testosterone the PCa “feeds” on. This level of cancer is usually way beyond surgery and radiation. The over a year PSA Velocity often can just be monitored to be sure it does not change. Often these men are old and likely to die from some other condition.

PSA Velocity is also being used to determine if there has been a relapse after surgery or radiation. While surgery removes the whole prostate, radiation can leave some surviving prostate tissue. This tissue can grow to replace the tissue “killed” by the radiation. This is now possible because of the advanced radiation techniques now available. These both direct the radiation beam to target only the cancer as the beam source is moved around the patient. The intensity of the beam is also varied as it is moved. All this is done to spare the adjacent tissues such as the rectum and urethra. While this would be uncommon, it would not be considered relapse if the PSA Velocity was a year or more. (As I remember from the relapse talk I heard.)

Note, my neighbor PSA Velocity was essentially zero, going from positive to negative from one test to another. So if the Urologist that he went to would have know how the interpret the test results, he would have not alarmed my neighbor unnecessarily. I don’t think he is going to that Urologist anymore.