Screening for Prostate Cancer

Should I be screened?

There is much debate as to the relative benefits and harms of looking for prostate cancer in men without symptoms. Several international organisations do not recommend screening, while others suggest an individual approach to screening.  The problems with screening are

  • To find prostate cancer requires a biopsy, which is invasive
  • Some cancers that are found are unlikely to be progress and probably can be left alone (so did not need to be found) (over diagnosis).
  • Some cancers are missed
  • Treatment of prostate cancer has side effects. (Overtreatment and harm)

The benefit of screening is that it does find early cancers that will cause problems and or death in the future and can be cured now. The difficulty is balancing the risks and harms inherent in screening for early cancer. The difficulty of screening for cancers with the risks of over-diagnosis and harm from treatment are not unique to prostate cancer.

What do health organisations say about screening?

Opinions are mixed. The American cancer society recommends that men make an informed decision weighing up the potential risk and benefits of screening for prostate cancer before having a blood test. http://www.cancer.org/cancer/prostatecancer/moreinformation/prostatecancerearlydetection/prostate-cancer-early-detection-acs-recommendations

The American academy of physicians recommends screening between 50 and 70 only http://annals.org/article.aspx?articleid=1676183

The American urology association suggests screening every second year in men 55-69, or 45-if at high risk http://www.auanet.org/education/guidelines/prostate-cancer-detection.cfm

The American Task force recommended against screening

http://annals.org/article.aspx?articleID=1216568&atab=7

As did this British review.

http://www.nejm.org/doi/full/10.1056/NEJMe0901166

For a balanced discussion see http://www.bmj.com/content/341/bmj.c4543.long

How do we screen for prostate cancer?

The starting point for screening for prostate cancer is a digital rectal examination (DRE) and a blood test called PSA. The PSA test should be taken when you are feeling well, and preferably not within 48 hours of sex or masturbation. If either test is abnormal then a prostate biopsy is usually recommended.

What studies have been done on screening?

If we look at the best international study on the subject (the European Randomised Screening Study) then looking for prostate cancer by a PSA test alone reduced the risk of dying from prostate cancer by 28% if you are screened. (In this study the risk of death from cancer was reduced by 20% if you were in the screening arm and 28% if you actually were screened as opposed to not screened). For the full report please see

http://www.nejm.org/doi/full/10.1056/NEJMoa0810084. In America a much smaller study was performed with significant problems of what is called contamination. That is in the "screened arm" about 25% of people were not tested and in the "not screened arm" about 40% of people in fact were screened. This study did not show a benefit to screening, probably because of size and contamination issues. http://www.nejm.org/doi/full/10.1056/nejmoa0810696

For a medical review of the issues please see:

What to do?

What is important I believe is to consider screening and treating in an intelligent fashion, so that we minimise the harm of screening. Then if a prostate cancer is found we should only treat important cancers (that is cancers of a higher grade or volume) while observing cancers which appear to be low grade (this is called active surveillance), thus trying to minimise the number of men treated.

If we do this, that is use the best modern tools available to screen, take a prostate biopsy after checking for bad bacteria and treat only those cancers which we think are important then I believe screening for prostate cancer is the correct thing to do.

How do we screen better?

  1. PSA test
  2. PSA/free ratio test and assess prostate volume
  3. MRI prostate if a biopsy seems necessary
  4. Take a rectal swab to screen for resistant bacteria before the biopsy
  5. Use the MRI to target the most likely sites for cancer
  6. Treat only those men who need to be treated.

What is PSA?

The first step in screening is a PSAtest and a rectal examination. PSA is a normal part of the male ejaculate or cum. It helps to break down the seminal clot so the sperm can swim away and try and find the egg. A tiny bit ends up in the blood stream and this can be measured. So it is normal for men to have PSA in their blood test. Many things one of which is prostate cancer increase the level of PSA but conversely some prostate cancers do not cause an increase in PSA. So a rectal examination to feel the surface of the prostate should also be done.

Given that the prostate makes PSA, the amount of PSA should relate to or be proportional to the size of the prostate. Now sometimes it is difficult to tell the size of the prostate but in general a good estimate of it can be made by a rectal examination. With this information one can estimate the risk of prostate cancer using a risk calculator. In general the easiest is to use the ERSCP risk calculator

http://www.prostatecancer-riskcalculator.com

Are there other blood tests I can have?

In addition to a standard PSA test it may be helpful to look at the PSA molecule in a bit more detail. In general I prefer my patients to a have what is called a free/total PSA ratio test. Because PSA is actually designed to eat proteins when it is in our blood stream it is usually attached to a protein that inactivates it. We can measure the amount of PSA bound to and not bound protein. For reasons that are unclear prostate cancer tends to release PSA that is more likely to be wrapped up in this protein, and this gives a lower PSA ratio test. In general PSA ratios below 12 indicate a high risk of prostate cancer and ratio tests over 21 a low risk of cancer.

Once the risk of potential cancer is determined by the PSA, ratio test and risk calculator then the next step if necessary is to do look at the prostate with x-rays to see if we can see any possible cancers.

What x-rays can help find prostate cancer?

Traditionally a prostate biopsy was performed without x-rays other than an ultrasound. A standard ultrasound (called a grey-scale ultrasound) does not usually see cancer, clever techniques such as elastography and contrast may improve the ability to see prostate cancers. At present however the best way to look for prostate cancers is with an MRI.  A special form of MRI called DWI allows us to see most prostate cancers.  The risk of a cancer is then graded 1-5 based on the pictures of the prostate.

MRI of the prostate can be used in one of two ways. If the chance of prostate cancer is low (based on PSA/prostate volume, DRE and PSA ratio test) then a biopsy is only done if there is a high risk of cancer as seen on the MRI (risk 4-5). If the risk of cancer based on blood tests is high then a biopsy will be performed if the risk is moderate to high (risk 3-5). Follow-up MRI's maybe required, as at this stage MRI of the prostate is still not 100% accurate.

Finally the biopsies taken can be concentrated on the regions that appear abnormal on the MRI. In the future biopsies maybe performed in the MRI itself but at present the MRI images are used to guide the ultrasound biopsy.

So you recommend screening?

In summary screening for prostate cancer makes sense if

  1. We use the tools available to decide on the risk of cancer
  2. Use MRI images when needed.
  3. Concentrate on taking biopsies from those areas that are abnormal on MRI and avoid biopsies from normal areas or doing biopsies in men who are at low risk of having cancer.
  4. Screen for bad bacteria before the biopsy.

I would like more information.

A detailed discussion on Prostate cancer screening can be found at

http://www.cancer.org/cancer/prostatecancer/moreinformation/prostatecancerearlydetection/index

A full discussion on the Canadian view

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3147035/

A New Zealand government view of this issue see

http://nhc.health.govt.nz/system/files/documents/publications/nhcprostatedocument.pdf