Saturday, September 19, 2009

Prostate Cancer Risk Screening

"Should I get a PSA test?" My patient was giving me a run for his money during his annual exam last week. We'd already discussed the pros and cons of undertaking treatment for blood pressure, and he'd asked for the evidence why one medication was preferable to another. He wanted to know if the data I presented was from studies sponsored by dirty drug company money. Finally, he threw out this challenge to conventional wisdom on prostate cancer screening, and a very good question it was.

Men anticipate prostate cancer screening with all the dread that women bring to Pap tests. Screening is generally limited to men over the age of 50 (unless there is a history of early prostate cancer in a father or brother) and consists of an exam of that part of the prostate that can be reached by a probing finger plus a blood test for prostate specific antigen or PSA.

The problem is that the PSA, while being the only cancer marker test currently available for screening purposes, is not specific. In other words, most men with an elevated PSA do not have cancer. The digital exam is even less specific as many aging men have enlarged prostates without harboring cancer. Other screening deficiencies in our current approach of one blood test and one finger exploration include:
  • Most men with prostate cancer (85% in one study) detected by PSA screening could avoid therapy. Per another study, one would have to screen 1400 men and perform 50 prostatectomies to prevent one death from prostate cancer.
  • There is no PSA level below which the risk of cancer is zero. The Prostate Cancer Prevention Trial (PCPT) found cancer in 6.6% of men with PSAs below .5 and 12.5% of those men had aggressive cancer.
  • Other factors seem to affect PSA levels, e.g. obesity and statin use lower PSA.
So what's a guy to do? One study over nearly 9 years showed a 20% decreased risk of cancer death with PSA screening every 4 years vs. none at all. Another concluded that testing every 6 years with digital exams every 4 made no difference whatsoever. Dr. Eric Klein notes(1): "All cases of prostate cancer are clinically relevant in that they can cause anxiety or can lead to treatment-related morbidity." In other words, we are detecting a large number of sub-clinical tumors--i.e. no symptoms suggest a prostate cancer brewing--with our screening, many of which would never cause a problem. We know that 90% of men with low-grade prostate cancer choose treatment which can cause incontinence, impotency, or death.

Dr. Klein suggests one approach to screening that uses seven variables to predict a man's risk of currently having prostate cancer. This test can be found at PCPT risk calculator.
1. Klein, EA. What's new in prostate cancer screening and prevention? Cleveland Clinic Journal of Medicine. Vol 76 August 2009 439-445.


Lee Smth said...

I think PSA testing is a good thing and all men should do it routinely by following the latest guidelines of the American Urological Association. That being said, I think Dr. Kleins predictive approach begs the question. I don't think we need a predictor of finding cancer via the biopsy, but rather what to do after that -- wait or treat? That predictor needs to take into account the biopsy results as well as the PSA, PSA velocity, etc.

Mauigirl said...

Interesting. Our family doctor does not recommend PSA testing as a general rule due to the limitations you cite.