PSA test for cancer screening: Good idea?

Should you get a PSA test to screen for prostate cancer? What are the advantages and disadvantages of screening? Do the potential benefits outweigh the potential harms? Those are the questions we will seek to answer in this article.

The problem is that prostate cancer is common, and for most people who have it, it is something that never causes any symptoms, and certainly not the thing that’s going to kill them. In medical school I was taught that the probability of having prostate cancer is about the same as the number of years you’ve lived. So, if you’re 50 years old, there’s a 50% chance that you have prostate cancer, and if you’re 80 years old, there’s an 80% chance. For most people, prostate cancer is a slow growing disease that never causes any problems. So, most people who have prostate cancer die with it, not from it.

PSA (prostate specific antigen) is an enzyme produced by the cells in the prostate. It was first discovered in the 1970’s and its biological function is to make semen more liquid after deposition in the vagina, freeing sperm to move around. It is normally present in low levels in the blood, but can increase to abnormally high levels in prostate cancer, due to the large number of cancerous prostate cells that are dividing in an uncontrolled fashion. This led to the idea that PSA could be used as a method to screen for prostate cancer, hence the PSA test.

The PSA test is simply a blood test, where you look at the level of PSA in a person’s blood. If the level is above a certain cut-off point, the value is considered “positive” (which is “positive” in pretty much the same way that being HIV-positive is “positive”), and that generally leads to a prostate biopsy being performed. And if the biopsy strongly suggests cancer, and there are no signs that the cancer has already spread throughout the body, then the prostate is usually either removed surgically, or irradiated. (If the cancer has already spread in the body, then it’s pointless to destroy the prostate – that only makes sense if there is still a chance at stopping the cancer before it spreads).

Now, for screening to make sense you need to be finding cancer in people who are going to die from it, at a point in the disease course when the cancer is still curable. The screening needs to change the course of the disease for the screened individual who has cancer, otherwise it’s meaningless.

Another aspect to screening is financial cost. From a societal point of view, the cost per case of treatable cancer discovered needs to be reasonable (at least if the tax payer is footing the bill). What a reasonable cost is, is of course something that each society needs to determine for itself.

A meta-analysis was published in the British Medical Journal in 2018 seeking to answer the question of benefits vs harms of prostate cancer screening definitively. The meta-analysis included five randomized controlled trials with a total of 721,718 men. The ages of the men enrolled ranged from 40 to 80 years old.

The screening interval varied across the studies, from a one time screening only, to once every two years, or even once a year, and the length of follow-up also varied, with the shortest follow-up period being 10 years, and the longest being 20 years.

So, what were the results? At the longest follow-up, 12,8% of men were dead in the group that received screening, and 12,9% were dead in the control group. This 0,1% difference was not statistically significant. Basically, PSA screening made no difference whatsoever to the odds of survival over the course of the follow-up period.

Now, let’s look at the negative effects of screening. As mentioned before, if the PSA test is considered positive, it gets followed up with a prostate biopsy before a decision is made whether to get rid of the prostate. One complication of this is a bacterial infection in the blood stream (sepsis). The reason you can get this complication is because the easiest way to reach the prostate with the biopsy instrument is by entering with it through the rectum, and then punching a hole through the wall of the rectum in to the prostate. When you do this, there is inevitably a risk that you will transfer bacteria that are living in the rectum in to the blood stream. Overall, 1,4% of men who were biopsied developed infections that were so severe that they had to be admitted to hospital.

If the biopsy result comes back positive for cancer, then in most cases that leads to surgery or radiation therapy, both of which pose a significant risk of impotence and urinary incontinence. The researchers calculated that, of 1,000 men screened, the screening will lead to a chain of events that will result in 25 more men becoming impotent and 3 more men developing urinary incontinence. How many of those men actually needed surgery or radiation therapy, i.e. had their lives saved by it? Probably not many, considering that the screening had zero effect on mortality.

Finally, we can look at what the review had to say about the diagnostic accuracy of the PSA test. Overall, the PSA test had a false positive rate of 67% . This means that 67% of men who have a positive PSA test don’t actually have any sign of prostate cancer when biopsied. The remaining 33% actually do have cancer, but we don’t know how many of them would ever have developed symptoms from their cancer before they died of other causes. Probably not many, or you would have expected to see an effect on mortality.

What does this all mean? Getting a PSA test for the purposes of screening is almost certainly a bad idea. The potential harms of PSA screening by far outweigh the potential benefits. While you’re considering whether to screen for prostate cancer, you might also want to consider how many blood pressure medicines you are taking, and whether statins make sense to take.

I am rolling out a ton of new science-backed content over the coming months, including:

- Analyses of the benefits and risks of all common supplements and medications
- The keys to a longer, healthier life (possibly quite different from what you may have heard)
- A long-term follow-up of the health consequences of the covid pandemic and global lockdown.

Please provide your e-mail address below and you will get all this content straight to your inbox the moment it is released.

Join 4,630 other subscribers

Author: Sebastian Rushworth, M.D.

I am a practicing physician in Stockholm, Sweden. I studied medicine at Karolinska Institutet (home of the Nobel prize in medicine). My main interests are evidence based medicine, medical ethics, and medical history. Every day I get asked questions by my patients about health, diet, exercise, supplements, and medications. The purpose of this blog is to try to understand what the science says and to translate the science in to a format that non-scientists can understand.

17 thoughts on “PSA test for cancer screening: Good idea?”

  1. So why are we doing it in the first place? Are you as a MD incentivized to propose PSA to patients?

    Primum non nocere.

    1. I’m not sure about other countries, but in Sweden where most doctors have a fixed monthly salary and no personal profit motive from PSAtesting, I don’t think that’s the reason. I think it’s more the case that a lot of people have been manipulated in to thinking it’s a good thing to get the test, and when they ask their doctors for it, it’s easier to just say yes than to explain why it might not be a good idea.

  2. Any Key Opinion Leaders passing by selling the message or luxurious confereces for the useful idiots, are those tricks real or exaggregated in the debate?

  3. I cannot believe this article is actually posted.There is ZERO correlation with psa scores and cancer.Its prostate specific antigen NOT cancer specific.The guy that discovered the process was Dr Richard Ablin…and he was so disgusted that it was hijacked for $ and not caner that he wrote a book on it…
    The Great Prostate Hoax: How Big Medicine Hijacked the Psa Test and Caused a Public Health Disaster Hardcover
    by Richard J. Ablin

  4. It appears that the PSA test itself is harmless, except for the cost. It is the response to the test that is the problem. Why not explain the risks to the patient of following up on a positive test and let him decide?

    1. Of course, that is also an option, and might make more sense in a US based medical system where the patient (or his private insurance) is footing the bill. In Sweden it makes less sense to even take the test, since it means a big cost to the tax payer thay results in zero benefit on overall mortality or public health. One problem I think is that a lot of people will have trouble living with the idea that they might have a cancer in their prostate, even though it will almost certainly not affect their life span, so if you get the test, that will probably result in removing a lot of prostates unnecessarily, even though you try to give the patient a balanced understanding of what the test implies.

  5. Sure, but the interviewed doctor seems very keen on the program. What is the responsibillity of the profession?

  6. My Doctor expand to me the pros and cons and backed it up with some good reading material. My question is, is there any other test one can do. Many years ago my doctor did the famous finger test. Does that mean anything ???? Thanks again for all your informative posts.

    1. Hi Herbert. There is no evidence to suggest that any form of screening for prostate cancer works, or that the benefits outweigh the risks. The reason for this is that most people with prostate cancer will never develop any symptoms from it, and will die of something else before the prostate cancer has a chance to make itself known.

      Screening is of course not the same thing as diagnosing the disease in someone who is symptomatic. If you have started to have symptomatic disease, then you do want to find and identify the cancer as soon as possible, and in that process it can make sense to take a PSA and perform a rectal exam to feel the prostate, as part of a wider investigation.

    1. The most common symptoms of prostate cancer are weight loss, blood in the urine, blood in the semen, bleeding from the rectum, problems emptying the bladder, back pain/skeletal pain (metastases from prostate cancer mostly end up in the skeleton).

Leave a Reply