Baseline CTC counts were shown to be strong indicators for subsequent therapy response and 2-year progression-free survival.
Data analysis of the SWOG S1216 trial showed that men with undetectable circulating tumor counts (CTCs) were 6.1-fold more likely to have a complete response to hormonal therapy and 3.7-fold more likely to achieve 2-years progression-free survival (PFS), according to study findings presented at the 2020 American Society of Clinical Oncology (ASCO) Virtual Scientific Program.
Amir Goldkorn, MD, an associate professor of medicine at the University of Southern California Keck School of Medicine spoke with CancerNetwork about the results of the trial.
So, this was a study that was conducted in the context of a large phase III randomized clinical trial called S1216. It's a trial run by the NCI Southwest Oncology Group, or SWOG, a multicenter study. The PI on the clinical trial aspect is Dr. Neeraj Agarwal of the University of Utah, and in this trial 1200 men were randomized to be treated with androgen deprivation therapy (ADT) plus either bicalutamide, an anti-androgen, or orterenel, which is a 617 inhibitor in a class similar to abiraterone. And what we looked at is basically drawing blood samples at the start of the trial and the patient's baseline blood samples for CTC counts, and looked at whether there was an association between the numbers of CTCs at start of study and whether the patients had a response to therapy and whether they had a long response. So, the response was defined as a drop in their serum PSA. The best possible drop at seven months is <0.2 ng/ml. And then there's 0.2-4 [ng/ml], or >4 [ng/ml], those types of drops are associated with having very good response to treatment and a good survival. The other thing we looked at is 2-year PFS. What we found was actually quite significant. The results of the studies showed that a man who had for example, zero CTCs, at baseline going on trial versus a man who had five or more CTCs if we compare those two types of results, the man who had zero CTCs going on study actually had a more than 6 fold odds ratio of having this complete PSA response in seven months on hormonal therapy. And conversely, the man who had the 5 or more CTCs at the start of the study had an almost 4-fold odds ratio of progressing his disease by 2 years. So very significant. In fact, it was significant when we looked at other comparisons like having no CTCs at all versus any or <5, versus >5. In all cases, it was highly significant as a prognostic factor. So overall, in this study, we found that CTC counts at the start of hormonal therapy were indeed prognostic for response to therapy and time to progression.