Measuring Circulating Tumor Cells Could Predict Prostate Cancer Treatment’s Success

What if you could count tiny particles of tumor in the bloodstream to predict whether a drug is working against cancer? Researchers in collaboration with the FDA are examining such tests as part of an effort to identify treatment efficacy to make clinical trials more efficient and less expensive, which could potentially lead to quicker FDA approvals.

The research team, led by Howard Scher, MD, of Memorial Sloan-Kettering Cancer Center in New York, investigated whether tests that trap circulating tumor cells (CTCs) could determine if patients with metastatic, castration-resistant prostate cancer responded to Zytiga (abiraterone), a drug that targets a protein in the production of testosterone, which can stimulate cancer cell growth. CTCs represent about one cell in a billion in the blood stream, Scher said.

Scher’s team examined a study of 1,195 patients in which Zytiga improved the median overall survival rate by 4.6 months. CTCs were tested in 972 patients at the beginning of the trial and at monthly intervals for three months. Researchers found a correlation in the reduction of CTCs and overall survival in patients on Zytiga.

Prostate cancer is common in older men, but the standard screening test for prostate-specific antigen (PSA) is unreliable because sometimes PSA rises even when a patient is benefiting from treatment, Scher says. Measuring CTCs may predict a better prognosis and overall survival as early as four weeks after treatment, as has already been shown in patients with advanced breast cancer receiving chemotherapy.