Is it time to consider PSMA PET scans in first line prostate cancer diagnostics?

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By Alan Doherty, Consultant Urologist, the Birmingham Prostate Clinic

The PSMA PET scan is now very widely accepted as a game changer in the management of recurring prostate cancer. At the Birmingham Prostate Clinic, we had our first experience of this new technology six years ago, when some of our patients chose to travel to Munich in Germany to access these scans, which were not available in the UK at the time. They were willing to travel because of the new perspective on early recurring prostate cancer these scans seemed to offer. I was pleased to contribute to this early study evaluating the effectiveness of PSMA PET scans in recurring cancer.

PSMA stands for Prostate Specific Membrane Antigen, a glycoprotein that sits on the surface of prostate cells and is increased if prostate cancer is present (especially if disease is metastatic). A small amount of a PSMA radiotracer is injected into the body and as this is taken up by the prostate cancer, it lights up on a PET (Positron Emission Tomography) scan. The clarity has astounded clinicians. It means we can see cancer spread within lymph nodes and identify tiny metastases of a few millimetres which may have occurred far from the primary cancer site.

Today, patients no longer need to travel to Germany for PSMA prostate cancer scans; for our patients at the Birmingham Prostate Clinic, the journey is to another site within our hospital group, at GenesisCare, Windsor. Among clinicians, even those who had a healthy cynicism about another ‘new thing’ in prostate cancer, there is now widespread acknowledgement of the high quality and value of PSMA PET scans.

Which leads us to another question – are we using them enough? Currently, PSMA scans are only regularly used in second line prostate cancer diagnostics and management: after there has been surgery or first line radiotherapy, but rising PSA suggests recurrence. PSMA scans are established as being useful for the cohort of patients with the type of recurrence which is not evident on a standard bone scan (we know, in reality, bone scans will only show advanced metastatic disease). Before PSMA prostate cancer scans, this cohort of patients were left with the uncomfortable knowledge that their prostate cancer had spread, but we couldn’t tell them where. PSMA changed all of that, providing ultra-sensitive scans identifying cancer spread even at very low levels of PSA increase (https://link.springer.com/article/10.1007/s12149-019-01400-6).

So, are we right, in the UK, in routinely using PSMA PET scans only after treatment and not in primary diagnostics? To take, for example, the patient cohort I have just described above:  high risk patients, with PSA of 20 or above, or above 10 with a high Gleason score. We treat these patients as if they do not have metastatic disease but we are doing so not because we are sure, but because our current diagnostic pathways do not allow us to see low level spread.

In Germany, PSMA PET are being used for some patients in first line diagnostics, typically where there is very high likelihood of prostate cancer being present and reasonable suspicion of spread beyond the prostate capsule. The view is that the extra level of detail from a PSMA PET scan is valuable when the patient is first diagnosed and treatment is being planned; before recurrence seems to have occurred. I believe in the UK, we need to reflect again on our diagnostic pathways for prostate cancer; whether we need to think again according to patient risk profiles and bring in the right technology at the right time for each individual.

References

Rauscher I., Doherty A., et al., Value of 68Ga-PSMA HBED-CC PET for the Assessment of Lymph Node Metastases in Prostate Cancer Patients With Biochemical Recurrence: Comparison With Histopathology After Salvage Lymphadenectomy. Journal of Nuclear Medicine 2016 Nov; 57 (11):1713-1719.

Schmidkonz C et al (2019) PSMA SPECT/CT with 99mTc‑MIP‑1404 in biochemical recurrence of prostate cancer: predictive factors and efficacy for the detection of PSMA‑positive lesions at low and very‑low PSA levels. Annals of Nuclear Medicine (2019) 33:891–898


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