Decline in circulating tumor cells during treatment associated with better survival

This study examined the link between circulating tumor cells (CTCs) and treatment outcome in metastatic castration-resistant prostate cancer (mCRPC). Authors reported better survival outcomes for mCRPC patients with a significant decline in CTC count during treatment. 

Metastatic castration-resistant prostate cancer (mCRPC) is prostate cancer than continues to spread despite standard hormone therapy. mCRPC is considered advanced and associated with rapid disease progression. Treatment of mCRPC has improved in recent years with newly developed, secondary hormone therapies and chemotherapies. One of the greatest challenges in the management of mCRPC is accurate assessment of response to treatment.

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 a link between CTCs and treatment response in mCRPC.

This study examined the results of two trials to analyze changes in CTCs after treatment. A combined total of 486 men with mCRPC were included. 364 men received either placebo (control substance with no active effect) or secondary hormone therapy with abiraterone (Zytiga). 122 men were undergoing first-line chemotherapy. CTCs were analyzed before and during treatment. All men had high CTC counts before treatment (5 CTCs or more per 7.5 ml of blood). Patients were followed for an average of 11.2 months.

The average overall survival (time from treatment until death from any cause) was 11.6 months. The type of treatment did not affect overall survival. Average CTC count before treatment was 19.5 cells per 7.5 ml.

At 4 weeks, 64.3% of men showed a decline in CTC counts of 30% or more in response to treatment. This remained stable at 8 weeks (65.3%) and 12 weeks (64.4%). A 30% CTC decline at 4 weeks was associated with better overall survival (average 14.4 months) compared to men who did not achieve a 30% CTC decline (average 7.9 months). Similar results were observed at 8 weeks and at 12 weeks.

13% of men showed a stable CTC count at 4 weeks (less than a 30% increase or decrease since first measurement). This was similar at 8 weeks (11.3%) and 12 weeks (12%). A 30% CTC decline was associated with a survival benefit over stable CTC. However, stable CTC count was not associated with a survival benefit over increasing CTC counts.

Men receiving abiraterone had better overall survival than men in the same trial receiving placebo. However, men with a 30% CTC decline had similar overall survival regardless of whether placebo or abiraterone was administered. 

Researchers concluded that mCRPC patients with high CTCs have a better survival outcome if they show a significant decline in CTC count during treatment.