Circulating PCa cells are a strong marker of response to chemotherapy.
CHICAGO—Circulating tumor cells (CTCs) in patients with castration-refractory prostate cancer (CRPC) may help predict how they will respond to chemotherapy, according to findings presented here at the American Society of Clinical Oncology annual meeting.
“For men with hormone-refractory prostate cancer, PSA is not an accurate predictor of response to chemotherapy early during the course of treatment,” said study investigator Jose Moreno, MD, clinical associate professor of urology at Thomas Jefferson University in Philadelphia.
“CTCs, on the other hand, are a robust predictor of response to therapy two to five weeks after the initiation of therapy. CTCs may be a good surrogate biomarker [that is] superior to PSA in CRPC.”
Dr. Moreno and his colleagues looked at CTCs in 240 men with metastatic prostate cancer that failed hormone ablation therapy. The mean age of the patients was 69 years and 17 men (7%) were African Americans. The researchers evaluated CTCs at baseline prior to chemotherapy.
Men with at least five tumor cells per 7.5 mL blood sample had a median survival of 11 months compared with 21 months for those with fewer than 5 CTCs per 7.5 mL sample. CTCs were enumerated with the CellSearch System (Immunicon Corp.) in blood drawn pre-treatment and monthly thereafter for 18 months. Of the 240 men, 142 were alive at a mean follow-up of 11.4 months.
Median overall survival for 40 patients (19%) with CTC counts below 5 cells per 7.5 mL after just two to five weeks of chemotherapy was significantly longer than that of 78 patients (38%) whose CTC counts remained above 5. The patients with CTC counts below 5 lived more than 20 months compared to those with 5 or more CTCs who lived only 10 months.
In contrast, PSA was not a statistically significant predictor of survival at this time point. CTC remained the most significant independent predictor of overall survival in multivariate analyses that factored in stage at diagnosis, age, ECOG performance status, Gleason score, lactate dehydrogenase, alkaline phosphatase and PSA levels.
The results for the 65-site trial showed that those men who underwent chemotherapy and whose CTC numbers declined had a more favorable prognosis. The magnitude of response to chemotherapy was reflected in the CTCs levels, and the numbers held up even after more than 20 weeks of treatment.