Map of life expectancy at birth from Global Education Project.

Wednesday, July 13, 2005

Getting Examined

Prostate cancer is the most common cancer in men in the United States. According to data from a cancer surveillance program called SEER, age-adjusted incidence rates rose by 108% from 1986 to 1992, and then fell sharply. (The incidence rises sharply with age, so the total incidence is not the same as your own risk, which depends on how old you are.) The incidence of diagnosed prostate cancer varies quite substantially by race, for unkown reasons. According to the National Cancer Institute, "For white men, the [age adjusted] incidence rate peaked in 1992 at 185.8 new cases per 100,000 men before dropping 27 percent to 135.3 new cases per 100,000 in 1994. Incidence in African American men peaked in 1993 at 264.7 cases per 100,000 before declining 11 percent to 234.4 cases per 100,000 in 1994."

Pretty strange, huh? Was there something in the water in the late 1980s, which wasn't there after 1992? That could explain the election of George Bush the first, and his failure to secure a second term, but it does not explain the changing incidence of prostate cancer. For that, we have a diagnostic test to thank, called the Prostate Specific Antigen (PSA). In the late 1980s, doctors sharply increased their use of the test, so they started finding more cancers; then, after they had found a good percentage of them, there were fewer out there still to find and the incidence fell. The fact is that a large percentage -- possibly a majority -- of men over 70 who die of other causes, who are autopsied, turn out to have prostate cancer. Most prostate cancers are "indolent" -- they grow very slowly, they are non-invasive, and they do not metastasize.

In other words, you officially have a disease, but you do not have an illness. You have no symptoms, you do not perceive that anything is wrong with you -- until you have the PSA test and the doctor tells you, "You may have cancer." "May," because having an elevated PSA level doesn't mean that you necessarily have cancer, it just means that you might. But now, all of a sudden, you are sick. You need a biopsy, which costs money, hurts, and scares the shit out of you. Maybe the biopsy is positive. Now you're really scared, because you officially do have cancer!

Of course, so do most guys your age, the difference is that you know about it. Unfortunately, the doctor cannot tell you whether your cancer is going to become metastatic and cause a very unpleasant death; or just sit there quietly for the rest of your life until you die at age 97 in a windsurfing accident. But you might die of cancer! So now you need surgery which can leave you incontinent of urine and unable to, uhh, you know.

By the way, there is absolutely no evidence that widespread prostate cancer screening has led to a reduction in prostate cancer mortality. As a matter of fact, there is no relationship between the rate of PSA screening in a given state or country and trends in prostate cancer mortality. Although the mortality rate did decline in the early 1990s, for reasons which are not terribly complicated but which slightly exceed the word count limit of the blogging format, it is implausible that this was related to PSA screening.

Perhaps it is not a surprise that oncologists think that men over 50 should be offered the PSA test -- it brings them lots of business after all -- but when your doctor offers you the test (or your spouses doctor, if you discuss such things with him), here's something you should know. The test misses a lot of high grade tumors which are, in fact, dangerous; and falsely signals the presence of tumors when there aren't any. According to a recent article by Thompson, et al in JAMA 2005;294:66-70 (the initials used to stand for Journal of the American Medical Association but now they don't stand for anything -- although the American Medical Association does stand resolutely for physicians' right to make a whole lot of money), of men who started out with normal PSA levels and were screened annually by PSA and that really fun procedure where the doctor sticks his finger up your ass, 65% ended up getting at least one biopsy, which according to the protocol was triggered by a PSA level over 4 nanograms per mililiter, a number I'm sure you really care about, or an abnormality found on digital rectal examination. Of these, about one fifth ultimately received a diagnosis of prostate cancer, of which about one quarter had characteristics indicating that they were very dangerous.

This study included a biopsy for all the participants at the end of five years, which enabled the investigators to find out what was really going on. With the commonly used PSA cutoff of 4.1 ng/ml, 21% of cancer cases would have been detected, and 6.2% of men without cancer would have had false positives, resulting in unnecessary biopsies. Note that as this age group included men as young as 55, the majority of them did not have prostate cancer, therefore most of the biopsies that were performed would have found no cancer. Lowering the cutoff to 1.1 ng/ml would have found 83.4% of cancer cases but 61% of men without cancer would have had false positive results, which essentially means the test would be useless.

Men in the United States have a 17.3% risk of being diagnosed with prostate cancer, but only a 3% risk of dying from the disease. Yet, of men who are diagnosed and undergo removal of their prostate gland, 35% have recurrence of cancer. As the authors note, "An inherent property of all screening tests is that they disproportionately enhance the detection of slower-growing cancers, because more agressive tumors have a greater likelihood of becoming clinically apparent between screenings."

So guys, you now have the info. Make your own decisions. Don't let anybody, even one with a white coat and a fancy degree, tell you what to do.

1 comment:

Unknown said...

Admin, if not okay please remove!

Our facebook group “selfless” is spending this month spreading awareness on prostate cancer & research with a custom t-shirt design. Purchase proceeds will go to, as listed on the shirt and shirt design.