Correlation between serum PSA and PSMA targeting 18F-Florastamin PET/CT parameters in patients with prostate cancer

Introduction: To evaluate the relationship between serum prostate-specific antigen (PSA) level and parameters from prostate-specific membrane antigen (PSMA) targeting ¹⁸F-Florastamin positron emission tomography/computed tomography (PET/CT).

Methods: We retrospectively reviewed ¹⁸F-Florastamin PET/CT images performed for staging, restaging, and response assessment in patients with prostate cancer between January 2020 and December 2021. The maximum standardized uptake value (SUVmax), peak standard uptake value corrected for lean body mass (SULpeak), and total tumor volume (TTV) were calculated for all ¹⁸F-Florastamin PET/CT images. The tumor volume was computed using 40% of SUVmax as the threshold. The TTV was the sum of the volume from all the PSMA PET positive lesions that could reasonably assumed to be from prostate cancer metastases. Serum PSA level was obtained within 2 weeks of the ¹⁸F-Florastamin PET/CT scan (two patients within 4 weeks; most on the same day as PET/CT). The PSA levels were categorized into the following subgroups: ≤ 20, 20.1–50, 50.1–100, and >100 ng/mL. From the response assessment cases, we evaluated the correlation of absolute and percentage changes between the serum PSA levels and PET parameters. All PET parameters were analyzed for correlation with PSA levels using Spearman’s correlation coefficients.

Results: Eighty-three ¹⁸F-Florastamin PET/CT images of 40 prostate cancer patients were included. The mean age was 72±10.7 years (range, 42 – 89 years). The median serum PSA level was 45.1±563.0 ng/mL (range, 1.3 - 2856.0 ng/mL). The median time interval between serum PSA level and ¹⁸F-Florastamin PET/CT was 2 days (range 0~22 days). The PSA levels were positively correlated with SUVmax (p<0.001, r=0.374), SULpeak (p<0.001, r=0.394) and TTV (p<0.001, r=0.527). In forty-one response evaluation cases, the TTV computed from the PET/CT images and PSA levels in serum showed correlation in both absolute (r=0.414, p=0.007) and percentage changes (r=0.406, p=0.008).

Conclusions: ¹⁸F-Florastamin PET/CT-derived parameters showed a significant correlation with serum PSA level. In response assessment, total tumor volume changes measured from PSMA PET/CT images showed correlation with serum PSA changes.

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