Correlating survival outcomes in patients with advanced prostate cancer with novel hyperpolarized 13C MRI metabolic imaging biomarkers.

Abstract

e15059 Background: Hyperpolarized 13C (HP 13C) MRI is a novel molecular imaging approach that detects aberrant aerobic metabolism, namely elevated rates of pyruvate-to-lactate conversion (kPL), in patients with advanced malignancies. Higher kPL has been shown to correlate with higher tumor grade among patients with localized prostate cancer (PC). This research sought to evaluate the correlation between kPL and clinical outcome measures in patients with advanced PC. Methods: Patients with metastatic or locally advanced PC (castration sensitive or resistant) were prospectively enrolled at our institution and underwent HP 13C MRI of one or more target lesions identified on prior conventional imaging. Voxelwise kPL values were computed in MATLAB using an inputless two site exchange model. kPL,median was defined as the median kPL value per-patient across all target lesions; kPL,kurtosis measured the tailedness of the kPL distribution per-patient. We retrospectively analyzed progression free survival (PFS) and overall survival (OS) in subgroups divided by metabolic activity below versus above cut-point (kPL,median <0.017 s-1 and ≥ 0.017s-1, respectively). Survival statistics were calculated using the Cox PH model. Results: Sixteen patients (6 with castration-sensitive and 10 with castration-resistant PC) were accrued. With a median follow-up of 22.0 months from the date of MRI, the lower-kPL subgroup had significantly longer median PFS (11.2 vs 0.5 months; p<0.01) and OS (NR vs 18.4 months; p<0.05) compared to the higher-kPL subgroup. By comparison, baseline serum PSA (PFS: p=0.19, OS: p=0.41) and LDH (PFS: p=0.60, OS: p=0.34) did not demonstrate a significant association with clinical outcomes. There was a strong negative correlation between kPL,kurtosis and OS (r = -0.75), and moderate negative correlations between kPL,median and OS (r = -0.45) as well as kPL,max with both PFS (r = -0.48) and OS (r = -0.54). There was no significant kPL,median difference between castration-sensitive and resistant subgroups (0.015±0.011 vs 0.016±0.006 s-1, p>0.8). Conclusions: HP 13C MRI-derived non-invasive metabolic biomarker kPL,median significantly correlated with clinical outcome measures in a retrospective analysis of patients with advanced PC, outperforming established serological prognostic markers PSA and LDH. Limitations include our small sample size, retrospective design, and heterogeneous patient population. Nevertheless, these encouraging preliminary results support further investigation of HP 13C MRI as a prognostic and/or predictive PC biomarker in multi-center prospective imaging trials. [Table: see text]