Theranostics and Prostate Cancer

Theranostics and prostate cancer, by Alan Doherty, consultant urologist and Dan Ford, consultant clinical oncologist, the Birmingham Prostate Clinic.

Theranostics

You may have heard of a new term in the prostate cancer field: theranostics. The word ‘theranostics’ has been created by combining the terms ‘therapeutic’ and ‘diagnostics’ because the concept behind it is precisely that; the merger of diagnostics and drug therapy to personalise medicine.

Of course, you would be right in thinking there is always something ‘new’ in prostate cancer, typically heralded with newspaper articles, studies and exciting claims. In fact, you would be wise to take this savvy approach; there is always something proposed as new and promising in prostate cancer. At the Birmingham Prostate Clinic, although we have always sought to offer patients access to proven, effective advanced treatments and assessments, we have avoided ‘jumping on the bandwagon’ of every new offer. Careful evaluation is always needed.

Early experience

We had our first experience of the diagnostic side of this approach in prostate cancer in 2015. It was for a specific cohort: patients who have had primary treatment (usually surgery) but have a rising PSA (prostate specific antigen), indicating there is likely to be disease relapse. For a significant number of these patients, the relapse occurs on a biochemical level which is not evident on standard scans.

We began a collaboration with a centre in Germany providing a specific type of PET scan for patients in this scenario. It involves injecting a substance called a radiotracer into the body which is preferentially taken up by cancer cells rather than normal ones. This provides a ‘trace’ of very small groups of cancer cells on a biochemical level that would otherwise not be evident. In prostate cancer, the most effective tracer for this is called Gallium 68, which binds itself to membrane (PSMA) expressed by prostate cancer cells.

The diagnostic information provided in PSMA-based scans enabled us to apply highly targeted radiotherapy (Stereotactic Ablative Radiotherapy: SABR) and achieve significant disease control, delaying hormone therapy.

The future of theranostics in prostate cancer

The concept of theranostics is based on not only the diagnostic approach we have seen in the PSMA-based scans but in applying the same knowledge of biochemical processes to treatment. 177Lu-PSMA like Gallium 68 is preferentially taken up PSMA on prostate cancer cells. It also delivers a therapeutic radioactive treatment to these cells.

The therapy, 177Lu-PSMA, has been used safely in advanced metastatic prostate cancer for around 3,000 patients overall, mostly in Australia and Germany. The largest study published thus far involves 500 patients (with castrate-resistant prostate cancer). Findings after three to four cycles of 177Lu-PSMA are as follows:

  • 40% show a reduction of more than 50% in PSA level
  • 30% show 0-50% reduction in PSA
  • 30% show progression despite treatment
  • Progression-free survival of 6-21 months
  • Overall survival benefit of 6-14 months

Theranostics and prostate cancer: impact

Should theranostics, therefore, be considered the ‘new big thing’ in prostate cancer? It is important to maintain the caution underlined at the start of this discussion, however, that said, theranostics does seem significant. Keeping in mind: although the outlook for men diagnosed and treated for early-stage prostate cancer is very good, the other side to the story is that many are treated late and one in three men will have biochemical relapse (rising PSA) within ten years. For this significant group, theranostics does seem to be important.

We have long recognised that it is unsatisfactory if a patient has rising PSA, but standard scans are not sufficient to identify the location of cancer spread. The patients we work with, who were initially willing to travel to Germany (PSMA-based scans are now available in London) wanted the opportunity to treat recurrence at an earlier stage with more precise, targeted treatment. This seems entirely understandable and underlines exactly why theranostics is potentially an impactful, valuable new approach.

At the Birmingham Prostate Clinic, although we do not currently provide theranostics, we do have patients who have had PSMA scans and we are exploring the establishment of a clinical trial. We are happy to provide advice and guidance to patients.