Imaging Prognosis of a Negative 68Ga-PSMA-1 PET Scan on Followup Studies

Introduction: The usage ⁶⁸Ga-PSMA-11 (PSMA) PET patients for initial staging and biochemical recurrence has been shown to have high positive predictive value, sensitivity and specificity.¹ Few studies have evaluated at the utility of serial PSMA-PET scans in patients with biochemical recurrence of prostate cancer. The goal of this study is to evaluate the imaging prognosis of patients with baseline negative PSMA-PET scans and to correlate the findings with prostate specific antigen (PSA) values at the time of imaging.

Methods: A query of all patients who have received PSMA-PET scans at IU Health since August 8, 2021 was performed. This yielded a total of 904 studies. Of these, 98 patients who had multiple PSMA-PET studies were selected for evaluation. The images, date of scans, final impressions and PSA values were used for evaluation. All studies were initially interpreted by a nuclear medicine fellowship trained radiologist. Any indeterminate impressions at the time of initial interpretation were reviewed by a fellowship trained radiologist at the time of the data analysis, and a final imaging diagnosis was determined based on follow-up imaging findings or surgical pathology. 1 patient was excluded due to an indeterminant study without follow-up imaging or pathology. 6 patients without available PSA values at the time of imaging were excluded from the PSA portion of the analysis.

Results: Of the 97 included patients, 14 never developed PSMA avid disease, 23 developed PSMA avid disease on follow-up imaging after a negative baseline, and 60 patients had positive disease at baseline. This yielded an NPV of 37.8% for a negative initial baseline study compared to follow-up studies (Table 1). Of the patients who never developed PSMA avid disease, 64.3% had a PSA of less than 0.5 and 85.7% had a PSA of less than 1 (Table 2) compared to 43.5% and 65.2% respectively in patients who developed PSMA avid disease after a negative baseline study (Table 3).

Conclusions: Based upon our findings, a negative PSMA-PET is a poor predictor of having PSMA avid disease on a follow-up exam in patients with biochemical recurrence. Additionally, although patients with a lower PSA value at baseline imaging had a lower prevalence of PSMA avid disease at baseline and on follow-up exams, it does not appear to be a good overall predictor of whether PSMA avid lesions will develop on subsequent exams.

• Download figure
• Open in new tab
• Download powerpoint