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Decline in Circulating Tumor Cell Count and Treatment Outcome in Advanced Prostate Cancer

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Key Points

  • In both trials, patients with a 30% decline in circulating tumor cells survived significantly longer than those with stable or increased numbers, whether at 4 weeks (14.4 vs 7.9 months), 8 weeks (15.4 vs 7.9 months), or 12 weeks (16.1 vs 9.7 months).
  • Importantly, a drop in the number of circulating tumor cells was a useful indicator of prolonged survival whether the treatment used was abiraterone, steroids, or chemotherapy.
  • If these results are confirmed in future trials, then a 30% decline in circulating tumor cells could be used to make a treatment decision earlier—helping patients start better treatments faster and discontinue drugs that aren’t working sooner.

A drop in the number of cancer cells detected in a patient’s blood could be the best indicator yet as to whether treatment for prostate cancer is working. A new study, published by Lorente et al in European Urology, shows that a 30% decline in a patient’s numbers of circulating tumor cells, could signify that the patient is benefitting from treatment.

Methods

Scientists at The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust, with international collaborators, analyzed blood samples from 486 men with advanced prostate cancer before treatment and then afterwards at 4-week intervals.

Patient samples were analyzed from two different trials where a baseline circulating tumor cell count as well as monthly follow-up counts were available.

One of the trials, COU-AA-301, was a phase III trial in which patients with advanced prostate cancer who already received chemotherapy were given abiraterone and prednisone or placebo and prednisone.

The other trial, IMMC-38, was a prospective trial in which patients with prostate cancer that had metastasized received chemotherapy.

Study Findings

In both trials, patients with a 30% decline in circulating tumor cells survived significantly longer than those with stable or increased numbers, whether at 4 weeks (14.4 vs 7.9 months), 8 weeks (15.4 vs 7.9 months), or 12 weeks (16.1 vs 9.7 months).

Importantly, a drop in the number of circulating tumor cells was a useful indicator of prolonged survival whether the treatment used was abiraterone, steroids, or chemotherapy.

Previous work had suggested that a low number of circulating tumor cells indicated a better prognosis. But this is the first study to prospectively test whether a percentage decline in circulating tumor cell number can distinguish between patients benefiting from treatment and those who may need to switch treatments.

If these results are confirmed in future trials, then a 30% decline in circulating tumor cells could be used to make a treatment decision earlier—helping patients start better treatments faster and discontinue drugs that aren’t working sooner.

Professor Johann de Bono, MD, PhD, MSc, FRCP, Regius Professor of Cancer Research at the ICR and consultant oncologist at The Royal Marsden, said, “For too long, patients suffering from advanced prostate cancer and their clinicians have had to face a frustrating wait to find out whether a new a new cancer treatment was working. This study raises the prospect that a patient could simply have a blood test within as little as 4 to 6 weeks after starting a new treatment to indicate whether they should continue or switch to another option.”

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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