An article and editorial in today’s edition of the Journal of the National Cancer Institute about prostate cancer screening highlight the differences between the messages of science and the expectations of the media and the public, and how the two intersect.
The end result is that the science message from the article may be converted into a bit more sensational story than suggested by the conclusions of the research. After all, talking about science simply isn’t sexy. Talking about how medical tests harm patients is a surefire way to capture the attention of the public.
The research, which is interesting and well done from a science point of view, deals with the difficulty we have getting our arms around the fundamental question of how many prostate cancers are diagnosed by screening for the disease to find it early that would otherwise not cause a man harm or death. This is what doctors call “over diagnosis.”
The paper starts out by noting that previous studies claim the over diagnosis rate for prostate cancer—which is the percentage of prostate cancers diagnosed that never would have been a problem for a man—has ranged from 25% to over 80% of cancers diagnosed by prostate cancer screening. That is a lot of men who apparently have no benefit from having been diagnosed with this disease.
The researchers then took a more careful look at the question of what the real number should be, by using different complex mathematical models and standardizing various definitions as part of the study. They found that from 42% to 66% of prostate cancers were “over diagnosed.”
The other interesting observation was that these cancers were diagnosed from 6.9 to 7.9 years earlier than would have been the case without screening. This is what we call “lead time bias.”
The conclusion? According to authors, “The precise definition and the population used to estimate lead time and over diagnosis can be important.”
The authors go on to say, “ The lead time and the likelihood of over diagnosis are quantities that are critical in the assessment of the likely benefits and costs of any screening test; yet, in the case of PSA screening, results have been variable and confusing. This article is the first, to our knowledge, to closely examine the reasons for discrepancies across studies. Our results clearly show that the context or population used to derive the estimates, the definition of lead time used, and the estimation methodology all have important roles.”
Now, I am not saying that this research isn’t good work. It is, and it is important work. But it is important to scientists who study this problem, and probably not very interesting to most of the lay public.
The editorial which accompanied the article did in fact go on to relate the study itself to the questions surrounding the impact of prostate cancer screening.
The editorialist concluded—as does the American Cancer Society—that we really aren’t certain how many men we are helping by screening for this cancer. Until the evidence is in, both the editorial and the American Cancer Society along with a number of other highly regarded professional and science-based organizations recommend that men review the pros and cons of prostate cancer screening with their doctors.
This question is important, because since the advent of prostate specific antigen testing (PSA) in the late 1980’s, there has been a considerable spike in the number of men diagnosed with prostate cancer. There was also an initial surge in deaths from prostate cancer in the United States after we began using the PSA test, followed by a substantial decline in prostate cancer deaths in this country that continues through the present day.
The problem is that we can’t specifically tie the two events together in a cause and effect relationship. The same trends have been seen in other countries that do not regularly screen for prostate cancer. There are also discrepancies here in the United States when you compare areas where men are regularly screened for prostate cancer and other areas where they are not. Death rates have been dropping under both scenarios.
In the meantime, long term (and I mean long term) clinical trials to find out whether or not screening for prostate cancer saves lives have been ongoing in the United States and Europe, and we are still awaiting the results.
On top of this dilemma we have the fact that we are ramping up the war against prostate cancer. We are employing new surgical techniques such as robotic surgery and engaging proton beams to treat the disease. These approaches may be saving lives, but we don’t know for certain which man actually benefits from these treatments. And they come at a not insignificant financial and personal cost.
Inevitably, as you treat a man for prostate cancer—especially an older gentleman who may have other significant medical condition—you run into situations that are not pleasant. Pain, bleeding, incontinence, and impotence are not uncommon. Surgical deaths do occur.
When we screen for a particular cancer, we want to know that we are helping more than hurting. We call this the “benefit vs. risk” ratio. When the benefits outweigh the risks, it’s a good thing because we save lives. Screening for breast, colorectal and cervical cancers on a routine basis are examples of effective use of screening.
On the other hand, if we hurt more than we help when we screen for a particular cancer, it is not a good thing. Prior studies suggested that was the case for lung cancer. Newer clinical trials are underway using CT scans to find out whether our current technology may improve that situation.
Prostate cancer screening may fall somewhere in between. There are strong voices on both sides of the argument whether or not prostate cancer screening works. That’s why the American Cancer Society recommends you have an informed conversation with your health care clinician before embarking on a course of routine annual screening with the PSA test and a rectal exam to look for prostate cancer.
Another factor we consider when making a screening recommendation is how many people will we treat where it wouldn’t have made a difference?
That may sound strange to some, because it is the commonly held belief that every cancer is a bad cancer that will cause harm. But that’s not quite true.
We have known for decades that there are several different types of cancers that may exist in our bodies but never become apparent to us or our doctors.
For example, we know that many people have thyroid cancer that in the past would never have been diagnosed and never caused harm. Now, with our newer methods to look at the thyroid gland, we are finding many more cancers. We may be diagnosing more thyroid cancer on a population basis because we can find them, but it isn’t clear that there are in fact more thyroid cancers being found that would have led to serious medical consequences if they had never been discovered in the first place.
We have also known for decades that prostate cancer was close to universal in men who approached the century mark in their lives. But those cancers were found incidentally at autopsy, and never caused a problem. Even men like me (I am not going to reveal my age here, but my hair is a bit gray) have a fairly high percentage of prostate cancer that would be found if one decided to go looking for it, even with a very normal PSA test.
So here we are on the horns of the dilemma which I mentioned earlier in this blog.
There are many, many men out there who firmly believe that prostate cancer screening saved their lives. There are many expert physicians who agree with them. There are many expert physicians who do not agree.
There are many hospitals and community organizations that regularly run “prostate cancer screening fairs” as a means of finding men with this cancer (who then go on to spend thousands of dollars at the hospital and/or the medical practice or elsewhere when they receive treatment for their prostate cancer).
But here is what we know and have known for some time:
We test a lot of men for prostate cancer. We find a lot of men with prostate cancer. There are many men we treat who probably would have been fine without finding their prostate cancer. There are many men we treat where our treatment didn’t make any difference, and they would have died from their prostate cancer no matter when we diagnosed it or how we treated it. There are some men we treat where finding the cancer through screening probably did save their lives. And for many of the men in each of these groups, we have changed the quality of their lives forever and not necessarily for the better.
The problem is we don’t know which men belong in which category.
So I come back to my initial thought: here is a well done research study published by reputable investigators in a reputable scientific journal that makes a legitimate scientific point. And the editorial expounds appropriately on the implications of the research relative to the impact of prostate cancer screening.
That’s important, but it isn’t really news to many of us familiar with this issue.
I suspect you will be hearing about this story and its implications in an entirely different context, and probably in a way that will cause you concern and lead you to ask questions that really in fact are not related to the primary purpose of the research. In fact, the reports may actually frighten many of you.
Hopefully the news stories will lead you or someone you love to have a better understanding of the controversy surrounding the “early” diagnosis of prostate cancer. Hopefully that will lead you to have an honest discussion with your doctor. Hopefully you will become more informed about this aspect of your health care. Someone who is informed about their health will likely be someone in better health.
Maybe that isn’t such a bad thing after all.
