SNMMI 2016: 11C-acetate PET/CT accurately predicts prostate-cancer specific survival in patients with biochemical relapse after prostatectomy

San Diego, CA. USA (UroToday.com) – 11Choline-acetate (11C-acetate) has been used as an investigational PET radiopharmaceutical to image patients with prostate cancer based on elevated transports in prostate cancers after prostatectomy to detect recurrence and metastasis upon biochemical relapse.  Its utility for predicting outcomes in this group of patients has not been reported.  Naresh Kumar Regula, from the Uppsala University, Sweden presented new data at the 2016 Society of Nuclear Medicine and Molecular Imaging annual meeting.  The question of whether parameters measured by 11C-acetate PET correlate with clinical outcomes including survival.

To answer this question, the Uppsala University researcher designed a retrospective analysis of all 121 post-prostatectomy patients with elevated PSA and undergoing 11C-acetate PET, including 22 with prostate-cancer specific death (Cohort 1) and the censored group of 99 (Cohort 2) over a median of 79 months. Post-operative Gleason sums(PS), PSA at time of PET,  SUVmax, tumor volume (using threshold of 30% of SUVmax), total tumor volume and total lipogenic activity (TLA=summed SUVmax*TV). Survival analysis was followed by Cox-proportional hazards ratios (HR) in patients with positive PET findings.

Comparison between the 2 Cohorts reveals significant 5-year survival benefit for a negative 11C-acetate PET.  Distal lymph node metastasis and bone metastasis are strong predictor of PCa-specific death.  Highest SUVmax, TTV and TLA are significant predictors for PCa-specific death.  PS, Tertile of highest SUVmax, tertile of TTV, tertile of TLA, numbers of distal LN metastasis and number of bone metastasis are significantly correlated with PCa-specific death under univariate analysis while multivariate analysis only find significance with PS, Tertile of TLA and numbers of bone metastasis.

11C-acetate is available to many countries including the USA as an investigative radiopharmaceutical for cancer detection, especially after initial therapy.  While awaiting further confirmation from prospective randomized trials, current findings indeed support the use of 11C-acetate PET in the care of post-prostatectomy patient upon biochemical relapse. 11C-acetate PET-CT may in fact serve more than mere recurrence detection by providing prognosis.  A negative 11C-acetate PET-CT in asymptomatic patients with PSA relapse after prostatectomy suggests an excellent 5-year survival. 

Upon questioning, the author answered that a relative threshold of 30% SUVmax was chosen to derive the tumor volumes which were used to calculate the TLAs.  He did not optimize the threshold because it is standard procedure as done by others.

Presented by the Team headed by Naresh Kumar Regula at the 2016 Society of Nuclear Medicine and Molecular Imaging annual meeting in San Diego, CA, USA. Abstract #521.

Written By: Franklin C. Wong, MD. PhD, JD,  Professor of Nuclear Medicine and Neuro-Oncology The University of Texas M. D. Anderson Cancer Center, Houston
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