Circulating tumor cells can predict treatment success with docetaxel

This study examined the predictive value of circulating tumor cells (CTCs) during docetaxel (Taxotere) treatment for metastatic castration-resistant prostate cancer (mCRPC). Researchers reported a strong association between CTCs and treatment response to docetaxel.

Hormone therapy is the standard of care for advanced prostate cancer, including prostate cancer that has spread to distant organs (metastatic). Over time, many men stop responding to standard hormone therapy, resulting in the cancer progressing and continuing to spread. This is known as metastatic castration-resistant prostate cancer (mCRPC). Treatment of mCRPC has improved in recent years with newly developed, secondary hormone therapies and chemotherapies. Docetaxel remains the first-line chemotherapy for mCRPC.

Once prostate cancer has advanced to mCRPC, predicting treatment success early on is increasingly important. Studies have shown that circulating tumor cells (CTCs) can be used to predict survival in patients with mCRPC. CTCs are cells from a primary tumor that have migrated into the blood stream. A higher CTC count is believed to be indicative of disease progression. However, further studies are needed to determine the predictive value of CTCs during mCRPC treatment with docetaxel.

This study analyzed CTC counts in 212 men undergoing treatment for mCRPC. Men were treated with docetaxel and prednisone (a steroid), either with or without additional atrasentan (Xinlay; an experimental cancer drug). CTCs were analyzed before treatment and after the first treatment cycle. Men were divided according to low CTCs (less than 5 CTCs per 7.5 ml) and high CTC (5 CTCs or more per 7.5 ml).

Men with higher CTCs before treatment had significantly worse bone pain, higher PSA (prostate specific antigen; a protein elevated in prostate cancer), more liver disease, and lower hemoglobin (protein responsible for transporting oxygen in the blood). Treatment response (based on PSA levels) was achieved in 63% of men with low CTCs. This was significantly greater compared to 44% of men with high CTCs. Treatment response (based on imaging of the tumor) was 31% in the low CTC group and 14% in the high CTC group.

Average overall survival (time from treatment until death from any cause) was 26 months among men with low CTCs and 13 months among men with high CTCs. Overall, men with low CTCs were 2.74 times more likely to survive the duration of the study. An increase in CTC levels between the two measurement times was associated with reduced overall survival (by about 47%). Similarly, a reduction in CTC levels improved overall survival (about 6.47-fold). Treatment response was also associated with a change in CTC count. 

Researchers concluded that CTC count is predictive of overall survival and docetaxel treatment response. An early rise in CTCs during docetaxel treatment may be an indication to switch therapy.