Platelets harbor prostate cancer biomarkers and the ability to predict therapeutic response in castration-resistant patients.
e583 Background: Novel therapies for castration resistant prostate cancer (CRPC) have been introduced in the clinic with possibilities for individualized treatment plans. Best practice of those expensive drugs requires predictive biomarker monitoring. This study used circulating biomarker analysis to follow cancer-derived transcripts implicated in therapy resistance. Methods: The isolated platelet population of blood samples and QRT-PCR were used to identify selected biomarker transcripts in patients with CRPC prior chemo- or androgen synthesis directed therapies. The association between biomarker status in platelets (positive vs. negative) and therapy response, progression-free survival (PFS) and overall survival (OS) was examined. Results: Fifty patients received either docetaxel (n = 24) or abiraterone (n = 26) therapy, with therapy response rates of 54% and 48%, respectively. Transcripts for the PC-associated biomarkers kallikrein-related peptidase-3 ( KLK3), androgen receptor splice-variant 7 (ARV7), folate hydrolase 1 (FOLH1), and neuropeptide-Y ( NPY) were present within the platelet fraction. Analyzing biomarkers in the chemotherapy group did not add information about PFS, but FOLH1 was associated with short OS (p = 0.00015). In the abiraterone treated cohort, detectable FOLH1 (p = 0.009), KLK3 (p = 0.018), and NPY (p = 0.028) were all associated with short PFS. Patients with biomarker-negative platelets had the best outcome, while FOLH1 and NPY provided independent predictive information regarding PFS and KLK3 (p = 0.001) and FOLH1 (p = 0.002) were associated with short OS. Conclusions: Analyzing tumor-derived biomarkers in platelets of CRPC patients enabled prediction of the outcome after abiraterone therapy with high accuracy. Platelet-based analysis of FOLH1, NPY, and KLK3 may be used for treatment stratification of patients scheduled for treatment with abiraterone.