Exosomal TUBB3 mRNA expression of metastatic castration-resistant prostate cancer patients: Association with patient outcome under abiraterone.

BACKGROUND

To use ddPCR to quantify plasma exosomal class III β-tubulin (βIII-tubulin, TUBB3, encoded by the TUBB3 gene) mRNA expression in metastatic castration-resistant prostate cancer (mCRPC) patients, and study the association of this expression with abiraterone efficacy.

METHODS

Blood samples were prospectively collected from 52 mCRPC patients using abiraterone as first-line therapy to measure plasma exosomal TUBB3 mRNA expression value before the initiation of abiraterone. Study endpoints were PSA response rate, PSA-progression-free survival (PSA-PFS), and overall survival (OS, from CRPC to death).

RESULTS

Patients with positive exosomal TUBB3 expression showed shorter PSA-PFS (negative TUBB3 vs. positive TUBB3: 11.0 vs. 7.9 months; p = 0.014). Further analysis demonstrated that patients with strongly positive exosomal TUBB3 (>20 copies/20 µl) was associated with even shorter PSA-PFS (negative TUBB3 vs. positive TUBB3 [<20 copies/20 µl] vs. strongly positive TUBB3 [>20 copies/20 µl]: 11.0 vs. 8.3 vs. 3.6 months, p = 0.005). In multivariate analyzes, TUBB3 (+) (HR: 2.114, p = 0.033) and ECOG score >2 (HR: 3.039, p = 0.006) were independent prognosticators of poor PSA-PFS. PSA response and OS did not present significant differences.

CONCLUSION

The exosomal TUBB3 mRNA expression level is associated with poor PSA-PFS of abiraterone in mCRPC patients. The detection of exosomal TUBB3 can be valuable in their management.