Screening & Diagnosis of Prostate Cancer
It is recommended that the process of prostate cancer screening be governed by a 'shared decision making' model.
This means that your input is required. You will need to invest some time to become informed in order to make consultation with your urologist efficient and productive. The urologist will assist you in making a decision (and may make a recommendation) but ultimately the decision is yours.
Be Aware of The Steps In The Screening Process
Decide if prostate cancer screening is right for you. Discussion can be initiated by the patient or physician.
If a patient consents to screening then a PSA and prostate exam are done. Both are necessary. PSA alone is not accurate enough to establish risk.
Risk assessment is completed and discussed.
You make a decision with assistance from the urologist. Be prepared to select one of the following options based on the risk assessment and your preferences:
Repeat the PSA and prostate exam at an appropriate time interval.
Secondary risk assessment (e.g. prostate MRI).
Prostate biopsy.
Discontinue screening altogether.
Go home and think about it.
STEP 1: Decide If Prostate Cancer Screening Is Right For You.
Most people assume that cancer invariably leads to death and that early diagnosis results in better outcomes. Prostate cancer screening can lead to early detection in some men. Early treatment can lead to longer life in some men. Treatment may not cause problems for some men. However, these outcomes do not occur in all men - sometimes an undesirable result occurs. There are several reasons for this but they all come down to the fundamental problem of predicting the future. The 3 primary characteristics of prostate cancer that make prediction challenging are:
Prostate cancer behavior can be unpredictable.
The cancer may never progress and cause any problems BUT can cause suffering and/or death.
The cancer may progress so slowly that a man dies of another condition before the prostate cancer has an opportunity BUT some men will live long enough that the cancer has an opportunity to cause suffering and/or death.
The cancer may have spread prior to diagnosis rendering it incurable and thereby removing the benefit of screening BUT evidence of incurability may only be apparent in hindsight - sometimes years after one must make a decision on whether to receive (or forego) radiation or surgery.
Prostate cancer surgery and radiation are double edged swords. Curative treatments for prostate cancer have the potential for benefit and harm. Occasionally the complications from the treatment can be devastating. Radiation and surgery can cause irreversible problems with:
Urinary function.
Sexual function.
Bowel function.
Life-expectancy is key. Life-expectancy can be challenging to assess. Men need to live long enough to benefit from treatment. Many men with prostate cancer will 'die with it instead of from it' without any treatment. Accurate assessment of life expectnacy is challenging over the 10+ year time horizon that prostate cancer screening requires to be of benefit.
Younger men are more likely to benefit from screening.
Older men are less likely to benefit from screening.
It bears emphasizing that screening and treatment of prostate cancer relies on prediction of the future. An inherent property of prediction is uncertainty. In the absence of certainty, the best that we can do is make educated guesses with the information at hand. Information also changes with time. This is not just a problem with prostate cancer screening but with virtually everything in life - the future is alwasy uncertain to some degree. In prostate cancer screening this results in an unavoidable tension between overdiagnosis and underdiagnosis which can, in hindsight, be a source of overtreatment and undertreatment. The aim is to strike the right balance for the each patient at a specific time in their life.
The following websites provide information on the pros and cons of screening. READ AT LEAST ONE OF THESE BEFORE YOUR VISIT.
Prostate Cancer Canada: Prostate Cancer Basics: Screening and Diagnosis
American Cancer Society: Testing for Prostate Cancer
American Society for Clinical Oncology (ASCO) Prostate Cancer Screening Decision Aid Tool
+ What is Screening?
Screening has two primary properties:
- Screening is a DIAGNOSTIC PROCESS which uses a series of TESTS. Like any other clinical decision making process, it is based on PROBABILITIES.
- When the probability of disease being present is close to 100%, the presence of disease is confirmed.
- When the probability of disesae being present is close to 0% the disease is ruled out.
- What defines screening as a unique diagnostic process is that it attempts to identify disease often when there are NO SYMPTOMS. The ultimate goal is detection of disease at an EARLIER STAGE then would occur through routine stage with the hope of BETTER OUTCOMES.
Many patients who have screen detected cancers ask why they don't have any symptoms. The reason is that by the time most cancers cause symptoms the chances of cure is very low. By it's nature, screening is meant to detect cancer at an earlier stage before symptoms develop when the cancer has a better chance of cure. If one were to wait until symptoms are present, the outcome would probably not be as good.
+ How Does Diagnostic Testing Work?
It is critical to understand the DIAGNOSTIC PROCESS is one of determining PROBABILITIES. While the goal is to be as certain as possible in a diagnosis, sometimes compromise is necessary.
An example of when compromise is necessary would be when the test which could confirm the diagnosis caries significant harm (for example, infection or bleeding). In these cases, treatment might be started without a definitive diagnosis - so long as the risks of the treatment were acceptable.
Fortunately in much of medicine the diagnostic process is fairly straighforward and results in a conclusive diagnosis - confirming (or excluding) the presence of a disease. Stated another way, the result is often 'black and white'. However, in some cases the degree of certainty is more 'grey' - that is, after a series of tests there remains uncertainty in the diganosis. In some cases it is impossible to entirely exclude the presence of a disease. In these situations there are significant consequences - this will become apparant when we look at prostate cancer screening.
TESTS are the tools that allow a clinician to determine the probability of a disease and ultimately reach a diagnosis. Testing takes many forms:
- history (symptoms)
- physical examination
- blood testing
- imaging (e.g. prostate MRI)
- genetic testing
- biopsy
An ability to select the best test from the toolbox (or series of tests) for any particular patient is what physicians are experts in. Selection of the test is important because for most tests there are a number of compromises in respect to diagnostic performance, cost and potential harm to the patient. For example, biopsies are usually highly accurate at establishing a diagnosis but tend to have higher risks for patients and are more expensive.
To say a test is 'inaccurate' is unhelpful since every test has at least some degree of 'inaccuracy'. Medicine is based in large part on quantifying the strengths and weakeses of every action that is taken. Medical studies and clinical trials are the powerful tools used to provide the evidence for the actions we take. Finally, a much neglected but important determinant of test performance is understanding how the test performs when it is used in various specific scenarios - this is often determines the ultimate value of a test.
The DIAGNOSTIC PERFORMANCE of a test describes how well the test does in assigning a probability that a disease is present. That is, how well it performs its primary function. ROC curves and likelihood ratios are 2 of the best measures. Measures such as accuracy, precision and false positives and negatives are more susceptible to the circumstances around testing and therefore are usually an oversimplification. There are multiple ways in which the performance of a test can be measured.
- Receiver operator characteristic (ROC) curves
- Likelihood ratios (also see here)
- Accuracy and precision
- False positive and false negative
Diagnostic performance is very different then the CLINICAL UTILITY of a test. Diagnostic performance doesn't take into account the costs or harms of a test. Furthermore, just because a test might show a statistical improvement in the ability to make a diagnosis does not mean that it will affect clinical decision making. Sometimes, increased diagnostic peformance does not translate into better results or change the recommendations for further testing or treatment. It is often said in medicine that 'statistically significant does not always mean clinically significant'.
Interpretation and application of test results, therefore, is highly CONTEXTUAL. For example, the interpretation of PSA depends on the circumstances - screening, after surgery, after radation, during chemotherapy, etc.
+ How Does Screening and Diagnostic Testing Work in Practice?
As discussed, screening is a diagnostic process that uses tests to reach a diagnosis in patients who do not have symptoms. There may be multiple steps in this process. Each step of the screening process can end at one of 2 places:
An actual diagnosis - either establishing the presence of a disease or ruling out the presence of a disease. Screening colonoscopy is a good example of this - if a tumor is seen, a biopsy can be taken immediately and a diagnosis can be made.
Identify patients who require additional or repeated testing ('Risk Refinement'). PSA for prostate cancer screening is an example of this. PSA rarely provides enough certainty to confirm a diagnosis. It can only help in the estimation of risk to determine people in whom prostate biopsy might be worthwhile.
The trade-offs in the 2 types of tests used in this example (colonoscopy vs. PSA) can be seen: colonoscopy is expensive, invasive with a small but definite risk of a serious complications but high accuracy; PSA is an inexpensive, easy blood test which has low accuracy.
Note that the language of risk and probabilities of a test is quantitative (based on numbers) but that decisions about whether it is worthwhile to proceed is ultimately a value based one. For this reason, the recommended approach to making that decision is called 'Informed and Shared Decision Making'. It is important that you understand the benefits and harms of screening tests and make an informed choice about which screening tests are right for you.
Just as any diagnostic process has limitations, so does screening. There are, however, some very specific limitations to screening:
- false-positive and false-negative tests results are possible
- screening can identify cancers which are not destined to cause any problems
- screening may lead to treatment which may not improve the person's health or help them live longer - in fact, the treatments may worsen their health or cause them to die prematurely
- screening tests can be harmful - while the needle poke needed to draw a PSA has virtually no risk, a perforated colon during screening colonoscopy can be life-threatening.
- screening can be expensive and divert limited resources from other worthwhile diseseases
As you can see, screening is not always a 'slam dunk'. Early detection can most definitely result in better outcomes for some patients but can also result in overdiagnosis and overtreatment in others. When the stakes are higher the decision process gets alot more difficult. This is the area where prostate cancer screening lives.
References:
Lange Textbook of Epidemiology
Cancer Screening Overview (PDQ) - Patient Version was originally publshed by the National Cancer Institute April 2017
STEP 2: Have a PSA and Prostate Exam
This part of the process is the most straightforward.
PSA is a blood test. Click here for information on Prostate Specific Antigen.
From a screening perspective, one should be aware that a confirmatory test is often necessary to confirm the accuracy of the test.
Prostate exam is an integral part of the process. It is sometimes called a DRE or digital rectal exam. DRE evaluates for prostate size, symmetry, nodularity, consistency (hardness or induration), margins and the status of the adjacent structures (seminal vesicles, rectum and pelvic muscles). Abnormal findings generally are not enough to confirm a diagnosis of prostate cancer but affect the risk that cancer is present.
STEP 3: You Will Be Provided an Estimate of Risk and Further Discussion
There is NO currently available test that can exclude the presence of prostate cancer with anywhere close to 100% certainty. The consequence is that every man has some risk of having prostate cancer. Cancer may be present even if the PSA is low, the prostate feels normal, if a prostate biopsy does not show cancer or if an MRI is normal - though all of these are associated with a lower risk of having cancer.
The only answer to the question "Do I have cancer?" can only be "Maybe". For some men, the 'maybe' is closer to 'very unlikely' but for others it maybe 'very likely'. It should be of some reassurance that by undergoing screening men are taking at least some control of that risk.
A equally vexing issue is that the only way to prove that prostate cancer is present is with a biopsy. The vast majority of men have nothing more than discomfort and recover quickly from biopsy but some may experience serious infection, bleeding or urinary retention.
Ultimately, we need a measure of risk so that you may make a decision. You will be provided an assessment of risk which will help you make a decision. Information that contribute to assessing risk of harbouring prostate cancer includes:
PSA
Prostate exam
Hereditary risk/family history
Biopsy history
Additional test results (e.g. MRI)
Other tests
Tools to evaluate risk and provide a quantitative assessment are available in the CaP Calculators section and are strongly recommended for clinical use. These calculators greatly outperform using any of the aforementioned pieces of information individually.
STEP 4: You Make a Decision
If you decided to undergo prostate cancer screening, you will ultimately need to select one of the following options (with the assistance of your urologist):
Repeat the PSA and prostate exam at an appropriate time interval (i.e. 'serial risk assessment/screening').
Secondary risk assessment (e.g. prostate MRI).
Prostate biopsy.
Discontinue screening altogether (may be appropriate in men with life-expectancies less than 10 years or very low risk of harboring cancer).
Go home and think about it. Take time for more thought/discussion about your options. Ensure you let your physician know your decision or if you require more discussion - it's your responsibility.
It's your health and this is why it is so important that you participate in the process. Your urologist has the expertise and experience to guide you but they can't make the decision for you.
Prostate Cancer Screening Guidelines
Many organizations have prostate cancer screening guidelines. These continue to change as evidence accumulates regarding the benefits and harms of screening and as the diagnostic testing continues to evolved.
European Guidelines (EAU-ESTRO-ESUR-SIOG). Highly recommended. The most up to date and comprehensive.
Canadian Urological Association Guidelines. Recommended. Very reasonable approach.
American Urologic Association Guidelines (AUA). As of 2019, these are becoming outdated. Does not integrate long term data on the ERSPC trial nor changes in diagnostic testing (e.g. MRI).
On The Web
Genetic testing for BRCA1, BRCA2: saliva test. Myriad Genetic Laboratories, Ambry Genetics and Gene Dx (2-4 weeks)
Deciding on When a Prostate Biopsy Should be Done