There is more evidence that the blood test used to count the number of cells circulating in the blood and shed from prostate tumors (circulating tumor cells or CTCs) can indicate whether a treatment is working or not working.
A major new study showed that the number of these circulating tumor cells in the blood predicted which if a man was benefitting from a prostate cancer treatment after beginning the treatment in as little as 12 weeks.
As tumors grow and progress, they shed some of their cells into the bloodstream, some of which can probably seed new metastases. So the researchers wanted to see whether a high number of circulating tumors cells was an indication of a growing tumor that wasn’t responding to treatment, and could predict a lower chance of survival.
Using circulating tumor cells to verify is a treatment is effective should allow doctors to switch men to an alternative treatment earlier than is currently possible. These results do need some more confirmation by further studies. Anther hidden possible benefit of using CTCs is that it might hasten the development of additional new treatments by speeding up clinical trials by using CTCs as surrogate biomarkers.
This study involved the detailed analysis of blood samples from 711 men who took part in a major phase III trial of the prostate cancer drug abiraterone.
The researchers measured numbers of circulating tumor cells at four-week periods after the start of treatment with the drug, along with a range of other biomarker molecules in the blood including lactate dehydrogenase (LDH), high levels of which are a sign of general tissue damage.
The trial itself had used the standard trial end points of average overall survival and survival free of cancer progression to show abiraterone’s (Zytiga) effectiveness in late-stage prostate cancer. But the researchers were able to cross-reference those results with data on circulating tumor cells and LDH levels in each man taking part.
They found a correlation between those men who had responded least well to treatment with abiraterone, and higher levels of cancer cells and LDH in the bloodstream, measured 12 weeks after starting treatment. They showed that levels of circulating tumor cells varied independently of a range of other biomarkers.
To prove the effectiveness of a new drug, clinical trials normally need to be run until the cancer is progressing clinically for each patient – and often until many of the patients on the trial have died. By using CTCs it might be possible shorten the time of clinical trials as well as shorten thr time we keep men on a treatment that is not effective.
H. I. Scher, G. Heller, A. Molina, G. Attard, D. C. Danila, X. Jia, W. Peng, S. K. Sandhu, D. Olmos, R. Riisnaes, R. McCormack, T. Burzykowski, T. Kheoh, M. Fleisher, M. Buyse, J. S. de Bono. Circulating Tumor Cell Biomarker Panel As an Individual-Level Surrogate for Survival in Metastatic Castration-Resistant Prostate Cancer. Journal of Clinical Oncology, 2015; DOI:10.1200/JCO.2014.55.3487
Joel T. Nowak, M.A., M.S.W.