ASCO 2017: Circulating tumour cells and survival in abiraterone and enzalutamide treated patients with castration-resistant prostate cancer

Chicago, IL ( Dr. De Laere presented a study investigating the prognostic value of circulating tumor cells (CTC) enumeration and dynamics in the context of second-line endocrine therapies (i.e. abiraterone or enzalutamide) in patients with metastatic castrate-resistant prostate cancer (mCRPC). 

This was a prospective multicenter study collecting blood samples from patients with mCRPC at baseline (n = 147) and follow-up (n = 95/147(64.6%)). At baseline, patients were stratified into favorable (< 5 CTCs/7.5mL) and unfavorable (≥5 CTCs/7.5mL) groups. Progression free survival (PFS) and overall survival (OS) were compared between groups. PSA changes at 10-12 weeks were also analyzed. 

Patients with ≥5 CTCs/7.5 mL (n = 59) at baseline had a PFS (3.9 vs. 11.3 months, p< 0.0001) and OS (9.34 months vs. not reached, p< 0.0001). Patients demonstrating increasing CTCs (n = 21) on therapy had a shorter PFS (4.03 vs. 10.36 vs. 13.08 months, p < 0.0001) and OS (11.2 months vs. not reached, p < 0.0001), compared to patients with decreasing (n = 41) and stable (n = 33) CTCs, respectively. Multivariable analysis showed that the number of CTCs (HR (95%CI): 1.0054 (1.0006–1.010), p= 0.0260) and an increasing follow-up CTC count (HR (95%CI): 2.8987 (1.2856–6.536), p= 0.0103) were independent predictors of PFS. CTC increase was the sole independent predictor for OS (HR 7.3512, 95% CI: 1.7953–30.101, p= 0.0055). At 10-12 weeks, a PSA response of ≥30% and ≥50% was achieved in 46/83 (55.4%) and 33/83 (39.8%) patients, respectively, which was statistically different between chemo-naive or pretreated patients (≥30%: p= 0.0395), patients with increasing, stable or decreasing CTC counts (≥30%: p= 0.0019; ≥50%: p= 0.0032), and patients with increasing or stable/decreasing CTC counts (≥30%: p= 0.0006; ≥50%: p= 0.0014). 

In summary, CTC levels are associated with PFS and OS in mCRPC patients, starting a new line of endocrine therapy. Follow-up CTC enumeration is associated with PSA response and its dynamics are an independent predictor of PFS and OS.

Presented By: Bram De Laere, MSc, Center for Oncological Research (CORE), University of Antwerp, Antwerp, Belgium

Written By: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Toronto, Ontario, Canada
Twitter: @GoldbergHanan

at the 2017 ASCO Annual Meeting - June 2 - 6, 2017 - Chicago, Illinois, USA