18F-fluciclovine PET/CT findings are predictive of failure-free survival following salvage radiotherapy in post-prostatectomy patients with biochemical recurrence.

1245 Objectives: Accurate detection of recurrent prostate cancer is important to improve the effect of salvage radiotherapy. 18F-fluciclovine is a novel PET radiotracer recommended for localization of recurrent prostate cancer post-prostatectomy. We examined the impact of fluciclovine PET on failure-free survival (FFS) following radiotherapy (RT) in patients with biochemical recurrence after radical prostatectomy. Methods: Seventy-nine post-prostatectomy patients (mean age 61.6±7.6 years, median prostate-specific antigen 0.33 [range 0.02-31.00] ng/ml) with biochemical recurrence in the experimental arm of a randomized controlled study comparing outcomes of RT guided by conventional vs molecular imaging underwent fluciclovine PET prior to RT ± ADT between October 2012-March 2019. RT was based on PET and clinical findings: no uptake or prostate bed only uptake - RT to prostate bed only, pelvic nodal uptake - RT to prostate bed+pelvis, extrapelvic nodal uptake - no RT. RT (median 66.6 Gy in 1.8 Gy fractions) was initiated 17±10 days after PET scan. Twenty-six patients received RT+ADT (median: 6 months). Patients are being followed up and evaluated after RT at predefined intervals; 4 weeks, then every 6 months for three years. 3 patients at 6 months, 2 additional patients at 12 months, 1 additional patient at 18 months, and 1 additional patient at 24 months post-RT were excluded from this analysis due to lack of follow-up. Treatment failure was defined as serum PSA ≥0.2 ng/ml+post-RT nadir followed by another higher value, a continued rise in the serum PSA despite RT, initiation of systemic therapy after completion of RT, or clinical progression. FFS based on fluciclovine PET findings were compared in patients that were 24 months or less post-RT. Results: 63/79 (79.7%) patients had positive fluciclovine PET findings. 4/79 patients were ineligible for RT due to systemic disease. Overall FFS at 6, 12, 18 and 24 months were 68/72 (94.4%), 59/65 (90.8%), 47/60 (78.3%), and 42/57 (73.7%), respectively. At 6 months (n = 72 patients), 16/16 (100%) patients with no uptake, 30/31 (96.8%) patients with uptake in the prostate bed only, and 22/25 (88.0%) patients with pelvic ± prostate bed uptake had FFS. At 12 months (n = 65 patients), 16/16 (100%) patients with no uptake, 26/28 (92.9%) patients with uptake in the prostate bed only, and 17/21 (80.9%) patients with pelvic ± prostate bed uptake had FFS. At 18 months (n = 60 patients), 13/14 (92.9%) patients with no uptake, 21/26 (80.8%) patients with uptake in the prostate bed only, and 13/20 (65.0%) patients with pelvic ± prostate bed uptake had FFS. At 24 months (n = 57 patients), 13/14 (92.9%) patients with no uptake, 19/24 (79.2%) patients with uptake in the prostate bed only, and 10/19 (52.6%) patients with pelvic ± prostate bed uptake had FFS. A significant difference in FFS following RT in patients based on fluciclovine uptake was noted at 24 months follow-up. Conclusions: Findings on fluciclovine PET/CT may be predictive of failure-free survival in post-prostatectomy patients with biochemical recurrence who have undergone salvage radiotherapy and may therefore have prognostic value. Longer follow-up duration and comparison to a control group not undergoing PET are required to fully evaluate the value of fluciclovine PET based radiotherapy. Funding:NCT01666808 / NIH R01CA169188, Blue Earth Diagnostics Ltd. provided fluciclovine synthesis cassettes.