This study evaluated the safety and feasibility of using hyperpolarized [1-13C]pyruvate for noninvasive characterization of tumor metabolism in patients with prostate cancer. The study involved 31 patients with biopsy-proven prostate cancer, who received injections of hyperpolarized [1-13C]pyruvate at three dose levels. The highest dose (0.43 ml/kg) was selected for further evaluation due to its higher signal-to-noise ratio. No dose-limiting toxicities were observed. Dynamic 13C magnetic resonance spectroscopic imaging (MRSI) data demonstrated the reproducible delivery of hyperpolarized [1-13C]pyruvate to the prostate and its conversion to hyperpolarized [1-13C]lactate. The 2D dynamic MRSI data distinguished signals from tumor and vessels, with a higher rate of [1-13C]pyruvate to [1-13C]lactate conversion in tumor. Single-time point MRSI data accurately reflected the presence, location, and size of cancer relative to surrounding healthy prostate tissues. The study confirmed the safety of hyperpolarized [1-13C]pyruvate and showed elevated [1-13C]lactate/[1-13C]pyruvate ratios in regions of biopsy-proven cancer, suggesting its potential for noninvasive cancer diagnosis and treatment monitoring.This study evaluated the safety and feasibility of using hyperpolarized [1-13C]pyruvate for noninvasive characterization of tumor metabolism in patients with prostate cancer. The study involved 31 patients with biopsy-proven prostate cancer, who received injections of hyperpolarized [1-13C]pyruvate at three dose levels. The highest dose (0.43 ml/kg) was selected for further evaluation due to its higher signal-to-noise ratio. No dose-limiting toxicities were observed. Dynamic 13C magnetic resonance spectroscopic imaging (MRSI) data demonstrated the reproducible delivery of hyperpolarized [1-13C]pyruvate to the prostate and its conversion to hyperpolarized [1-13C]lactate. The 2D dynamic MRSI data distinguished signals from tumor and vessels, with a higher rate of [1-13C]pyruvate to [1-13C]lactate conversion in tumor. Single-time point MRSI data accurately reflected the presence, location, and size of cancer relative to surrounding healthy prostate tissues. The study confirmed the safety of hyperpolarized [1-13C]pyruvate and showed elevated [1-13C]lactate/[1-13C]pyruvate ratios in regions of biopsy-proven cancer, suggesting its potential for noninvasive cancer diagnosis and treatment monitoring.