When prostate cancer patients no longer respond to hormonal therapy they are said to have castration-resistant prostate cancer (CRPC), an aggressive disease. Some of these patients die within a few weeks, while others survive up to several years. Today there are no methods to predict the prognosis of an individual CRPC patient, or how he will respond to treatment.
However, research now shows that such predictions could be made by measuring circulating tumor cells (CTCs), cancer cells that have broken away from a tumor and entered the bloodstream. According to an Memorial Sloan Kettering study led by medical oncologist Howard I. Scher, Chief of the Genitourinary Oncology Service; Martin Fleisher, Chair of the Department of Clinical Laboratories; and biostatistician Glenn Heller, CTC counts could help physicians in making treatment decisions and facilitate clinical studies. The findings were published in the February 11 issue of Lancet Oncology. [PubMed Abstract]
Increased levels of CTCs have been linked to poor outcomes in patients with prostate, breast, and colorectal cancers, both before and after a new therapy has been started. A test for measuring CTCs in blood samples is now being used for clinical management in patients with such cancers. To demonstrate how this test could be applied to monitoring patients with advanced prostate cancer, Dr. Scher and colleagues analyzed 164 CRPC patients who were beginning their first chemotherapy treatment.
According to the study, CTC counts were useful both in determining prognosis and in identifying which patients were benefiting from treatment. “Knowing that a treatment is not working allows us to change therapy sooner and to assess quickly whether the new therapy works better for that patient,” Dr. Scher explained. He added that blood levels of PSA — a protein that is measured routinely to monitor prostate cancer — are inadequate for making such predictions in CRPC patients.
The investigators also showed that CTCs, if measured during clinical trials, can help researchers in estimating how effective a treatment is before survival rates can be determined. “As a substitute for measuring survival,” Dr. Scher said, “the CTC number can accelerate drug approval, but this will need to be validated in future clinical trials.”