If you had prostate cancer (PCa) and opted to be treated with either prostatectomy (surgical removal) or whole-gland radiation, what sign of recurrence would you watch for? You’d be sure to have an annual PSA blood test. Why? Because after whole-gland treatment, it is expected that your PSA will drop to zero (or very close to it) and stay there.

PSA stands for Prostate Specific Antigen. Antigens are proteins on the surface of cells that are shed into the bloodstream. They are called biomarkers because these tiny substances come from prostate cells as well as prostate cancer cells. They can be measured in the blood, and they mark changes in cell activity. The more the cells are stimulated, the more PSA is shed. Many things can cause PSA shedding: infection, inflammation, riding a bike, non-cancerous gland enlargement, PCa tumors, even a digital rectal exam!

So, if you have no more prostate gland due to prostatectomy, or you have a destroyed gland due to radiation, there’s nothing left to shed PSA. Zero gland equals zero PSA. On the other hand, if some prostate cancer cells escaped the surgeon’s scalpel or survived radiation, there’s a chance they will colonize some other tissue in the body and grow into a new prostate cancer tumor. If this happens, it is called recurrence (the cancer is back) and it too will shed PSA into the blood.

Therefore, if a blood test registers a rising PSA after treatment, it is a “sign” of possible PCa recurrence.

Is there a better way to track for recurrence?

After whole-gland PCa treatment, the PSA test may be the first sign of recurrence, and it’s quite reliable.

However, we can’t count on PSA after a focal treatment like Focal Laser Ablation (FLA) to accurately signal recurrence. Since healthy cells remain in place, they will continue to shed PSA into the bloodstream. Yet the proportion of healthy tissue that is not treated by FLA differs from one patient to another, so “… PSA levels are less reliable in patients treated with FT due to a variable reduction in prostate volume post-therapy.”^[i] This means two things:
a) After FLA, the PSA blood test will never reach zero, and will often register 1 or higher; and
b) A rising PSA after FLA does not necessarily mean cancer is back, just as a regular annual PSA screening test may signal other prostate stimulation or activity.
Is there a better way than PSA to track for PCa recurrence after FLA?

A new study explains how imaging fits the bill

Thankfully, there is. Prostate imaging using multiparametric MRI (mpMRI) is a noninvasive method to track for recurrent disease. A newly published study out of the University of Toronto (Paxton et al., 2021) reveals how three imaging sequences (parameters) can identify telltale features of PCa arising in the prostate after ablation.^[ii] These three parameters are the same ones we use at the Sperling Prostate Center to detect PCa before treatment, and monitor our patients over the years following our FLA procedure:

• T2 weighted MRI
• Diffusion weighted MRI
• Dynamic contrast enhanced MRI

For their analysis, the Paxton study’s authors used data from 54 PCa patients whose cancers were treated with FLA between 2010 and 2014. Over that 4-year period, as their diagnostic and monitoring protocol became more refined, not all of the men were monitored in exactly the same way. Just over half of the cases (54.5%) had early mpMRI monitoring (4-8 months after FLA), while late follow-up mpMRI monitoring (up to 54 months after FLA) occurred with 84% of cases. Also, follow-up biopsies were not all done by the same method, and the authors acknowledge that the small size of the study plus the lack of identical protocols are limitations.

Still, there was sufficient data in terms of PSA blood levels and positive biopsies to correlate with image-based findings. This enabled the authors to identify particular tissue and anatomic features that were highlighted by each imaging sequence among those who had positive follow-up biopsies (significant PCa recurrence). They found that early mpMRI follow-up detected tissue artifacts that were the product of ablation-related scarring, which can obscure or confound clues to residual or recurrent PCa. Even so, in when early biopsy findings were paired with early MRI scans, imaging identified one of four patients diagnosed with clinically significant PCa.

On the other hand, the authors record that at late follow-up, two specific MRI traits, hyperenhancement and restricted diffusion, revealed recurrence at the treatment site in 63% and 83% of biopsy-proven recurrence, respectively. Notably, PSA change was not linked with either early or late biopsy results, so it would not have been reliable.

Given their findings that, “Late mpMRI was sensitive at detecting recurrent disease,” we can see how integrating suspicious post-FLA PSA blood tests with the clarifying power of mpMRI before rushing to biopsy is not only common sense, it’s far more accurate than rushing to conventional biopsy based on a rising PSA. The study team call this “reliable outcome data.” If mpMRI reveals areas of possible PCa recurrence, a real-time MRI-guided targeted biopsy provides precise diagnosis with minimal needles. To sum up, mpMRI has a valuable role to play in tracking possible PCa recurrence after FLA. In fact, it serves the same purpose after any focal treatment.

The Sperling Prostate Center now offers the three most advanced, FDA approved focal treatment for appropriate patients: Focal Laser Ablation, TULSA-PRO, and Exablate MRI-guided Focused Ultrasound. Contact us for more information and to learn if you are a candidate.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.

References

[i] Paxton M, Barbalat E, Perlis N, Menezes R, Gertner M et al. Role of multiparametric MRI in long-term surveillance following focal laser ablation of prostate cancer. Br J Radiol. 2021 Jul 29;20210414.
[ii] Ibid.