What is the role of cell-free circulating tumour DNA (ctDNA) in the treatment of metastatic prostate cancer (mPCa)? How do we treat oligometastasis? These were some of the questions raised during Plenary Session 12 “Current dilemmas in the management of metastatic prostate cancer” which was chaired by Prof. Hein Van Poppel (BE), Prof. Silke Gillessen Sommer (CH) and Prof. Peter Hoskin (GB).
“There is a strong unmet need for prognostic and predictive biomarkers to guide treatment of mPCa. We have this increasingly congested therapeutic landscape and a shift in consensus on when and how to best use these therapies,” said Assoc. Prof. Alexander Wyatt (CA). “How do we determine the optimal therapy and sequence of therapies for patients? Can tumour molecular subtype (genomics) help guide these decisions?”
In his lecture “Cell free DNA in blood: The best source for response prediction?”, he stated that one of the strengths of plasma cell-free DNA analysis is that all patients are eligible for blood-drawing; while with metastatic tissue biopsy, some patients may ineligible e.g. patients with aggressive diseases that have rapid deterioration.
According to Prof. Wyatt, serial sampling is more advantageous in a liquid biopsy setting as it is less complex. However, ctDNA does not provide information in all patients. “Another potential benefit of ctDNA is that it captures information from multiple metastatic sites while tissue biopsy which informs from a single metastatic lesion only. On the other hand, if a tissue biopsy can provide a very high-resolution of that single lesion, it will allow us to understand what is going on in a single metastatic site as ctDNA homogenizes heterogeneity. ”
In his lecture “Why do some patients only get oligo-metastatic disease?”, Dr. Ganesh Palapattu (US) emphasised treating the patients, not the diseases. “Not all prostate cancer patients are the same. Now we are treating fewer low-risk patients, and that is a good thing, and more high-risk cases. We’ve learned that there is a significant benefit for risk-based treatment allocation. We can’t treat all patients the same way. The diseases don’t behave in the same way.”
According to Dr. Palapattu, the term “oligometastasis” was originally coined by Dr. Samuel Hellman and Dr. Ralph Weichselbaum, and defined it as “An intermediate state of cancer spread between localized disease and widespread metastases”.
He stated, “If we’re going to treat oligometastasis effectively, we need to think about three main things: treat the primary because it is the important source of cancer cells; treat the metastasis that we can see; and treat the ones you can’t.”
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