Can MRI data improve decision-making about the need for a biopsy?

Last week we noted that adding MRI data to the Partin tables and to the Kattan/MSKCC nomograms did not seem to improve the accuracy of prognosis of outcomes after radical prostatectomy.

By contrast, a new report just published by Bhat et al. in Urology (“the Gold Journal”) suggests that the use of MRI-based PSA density data can be used to improve the accuracy of prediction of clinically significant prostate cancer in biopsy.

It is important, in thinking about this paper, to appreciate that the volume of a prostate, as measured using MRI scanning techniques, is a good deal more accurate than the volume of a prostate as measured using a trans-rectal ultrasound (TRUS) scan.

What Bhat et al. did was to go back and look at their database of 372 men who had all had a prostate MRI at Washington University between September 2014 and December 2016 (excluding patients already on active surveillance) and who went on to have a prostate biopsy. They then used this information to create six different models designed to predict whether a man would have clinically significant prostate cancer on biopsy.

Clinically significant prostate cancer was defined as the presence of any amount of Gleason 7 disease. The six different models were based on:

  • MRI-defined PSA density alone
  • PSA level alone
  • The Prostate Cancer Prevention Trial (PCPT) risk calculator alone
  • MRI-defined PSA density + MRI interpretation
  • PSA level + MRI interpretation
  • The PCPT risk calculator + MRI interpretation

Basically “MRI interpretation” means the patient’s PI-RADS score.

What Bhat et al. were able to show was  that:

  • MRI-defined PSA density alone was significantly better at predicting risk for clinically significant prostate cancer on biopsy than either PSA alone or the PCPT risk calculator, and that
  • The MRI-defined PSA density + MRI interpretation was significantly better at predicting risk than either the PSA level + MRI interpretation or the PCPT risk calculator + MRI interpretation

The ability to predict risk of a clinically significant prostate cancer on biopsy is an important factor in determining whether a man really needs a biopsy at all. And being able to provide a man with an accurate estimate of that risk is a key to shared decision-making about whether a specific patient wants to have a biopsy or would prefer to not have a biopsy and just continue to monitor his PSA level.

In their paper, Bhat et al. estimate that, by using MRI-defined PSA data + MRI interpretation, for every seven patients on whom they base a decision to recommend a biopsy, they are potentially able to either

  • Diagnose one additional case of clinically significant prostate cancer or
  • Successfully avoid one unnecessary biopsy in a man with who has a benign prostate or low-risk prostate cancer

These are by no means insignificant numbers.

Now, to be clear, what Bhat et al. have also shown is that the use of this potential prognostic tool only seems to work in men who are biopsy naive. In other words, you can’t use this system to tell whether a man who has already had one or more negative biopsies really needs to have another one, and you may not be able to use this method to determine whether a man who is already on active surveillance with low-risk prostate cancer needs to be re-biopsied for risk of clinically significant prostate cancer. (However, the latter was not tested in this study.)

It seems probable to The “New” Prostate Cancer infoLink that the next step in this process should be validation of the Washington University findings through the use of an independent set of MRI and related data. If these data can be validated using a separate set of data, it would then be helpful for potential patients and their physicians if these data could be used to create a predictive tool that was accessible on line in the same way as the PCPT risk calculator and the Kattan/MSKCC nomograms are. It would also help if the validation process could include validation of the actual findings when men went on to have a radical prostatectomy. In other words, if one could clearly show that:

  • The MRI-defined PSA data + MRI interpretation predicted risk for clinically significant prostate cancer on biopsy.
  • The presence of clinically significant prostate cancer on biopsy (or not) was confirmed by the pathological outcomes among those patients who went on to have a radical prostatectomy.

It could be difficult to do the second part of this validation in a world when many patients now don’t get a radical prostatectomy if they are on active surveillance for low-risk disease, but there may be large enough series of historic patients who had MRIs, were diagnosed with low-risk disease, and yet still decided to have a radical prostatectomy at some institutions.

5 Responses

  1. Thank you for reviewing this paper and highlightling the potential benefit of the PSA density calculation from prostate volume calculations determined on prostate MRI. This make perfect sense because the total PSA is related to the prostate volume and needs to be adjusted as such.

    While we are on the subject of prostate MRI, perhaps this would be an appropriate time to mention two 2018 studies by Pinto and Reiter that looked at the sensitivity of prostate MRI, comparing pre-operative prostate MRI findings with whole mount surgical findings. The results were a bit surprising and at the same time disappointing in that prostate mpMRI sensitivity was 50to 60%, missing 30% of cancers (10% were 1 cm or less). Reiter went on to say that the prostate mpMRI is not sensitive enough to be used to follow patients on active surveillance and that prostate biopsies will continue to be needed on a regular basis to monitor patients.

    This new information needs to get out to patients because one could develop a false sense of security with the high tech hype of getting targeted fusion mpMRI biopsies which are becoming increasingly available. This is better than blind biopsies for sure, but one needs to put it in perspective and continue to be vigilant.

    Hopefully, something even better will come along soon. It would not be surprising if we heard about these new breakthroughs right here. Thank you for keeping us up to date.

  2. Another detail not previous mentioned about the Pinto and Reiter articles is that mpMRI of the prostate underestimates the size of the cancer by two-thirds, meaning we are only seeing one third of the cancer on MRI. This has potentially serious implications for people who have undergone or are considering focal therapies for prostate cancer.

    The sitemaster might consider formally reviewing these articles for all to see. Thank you.

  3. Dear Walter:

    The issue of how frequently biopsies are necessary in men on active surveillance who are being monitored annually on MRI is a very complex one, and highly case-dependent. In other words, this is why there is no “one size fits all” about how often a man should be getting a repeat prostate biopsy if there is no other signal of the need for such a biopsy.

    Just to give you a couple of key pieces of guidance:

    — The original Johns Hopkins AS study clearly proved that annual biopsies are unnecessary, but, on the other hand, …
    — Most experts in AS get uncomfortable that an AS patient wouldn’t have a repeat biopsy within 3 years of his initial diagnosis and placement on an AS protocol

    However, the question of how often men who have been on AS for 10 years need yet another biopsy is not at all clear because if you have been stable on AS for 10 years without any meaningful rise in your PSA, without any change in your DRE, and without any sign of progression on an annual mpMRI and (say) four repeat biopsies over 10 years, then there have to be some real questions about often you are going to need additional repeat biopsies.

    Did you see this recent report on a presentation by Klotz last weekend?

  4. Dear Walter:

    I think we need to distinguish carefully between the detection of prostate cancer in a patient and the detection of individual lesions in a patient with prostate cancer. These are not the same thing.

    We also need to be clear that The “New” Prostate Cancer InfoLink has long been clear that you cannot use mpMRI scans to diagnose prostate cancer and that you cannot use targeted biopsies alone to accurately diagnose prostate cancer. The most appropriate form of diagnosis (when it is really necessary) combines an MRI scan with a TRUS scan to conduct a 12-core systematic biopsy along with additional biopsies of suspicious lesions evident on an MRI scan.

    From a patient perspective, the single most important thing for a patient to do is make sure that — if humanly possible — he is getting guidance from an experienced prostate cancer specialist (who is very often a urologic oncologist and not just a general urologist) who is aware of all of these issues and is therefore customizing the tests and the care s/he provides to the needs of the individual patient.

    The role of mpMRI (or biparametric MRI) in determining who is and who isn’t a good candidate for focal therapy is a quite separate issue, and at present I am not aware of any formally approved form of focal therapy for prostate cancer, so the numbers of patients who are receiving such treatment remains very small. Once again, the critical issue today is for patients who are interested in focal therapy to be seeking out experienced practitioners of this type of therapy and then asking lots of questions. There is no good “one size fits all” set of guidance that one can offer such patients at this time.

    With regard to the selection of the articles we decide to “formally review”, you need to appreciate that it is no longer possible for anyone to review on a formal basis even all of the important data that gets published each year. Last year alone, Dr. Reiter was an author on 14 papers and Dr. Pinto was an author on another 20. They are just two of the probably 500+ “heavyweight” authors of new papers each year in the field of prostate cancer. If each of those authors (with his or her colleagues) is publishing about 15 papers a year, that’s 7,500 papers a year or 20 papers a day! And that doesn’t include all the papers from those who publish less often but who may be offering very valuable insights.

  5. Thank you for weighing in on the questions that were raised. We are very fortunate to have such an excellent site to look to for insights on this very challenging problem, PCa.

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