Abstract
1448
Introduction: Prostate cancer is the most common solid malignancy in men and the third leading cause of cancer related death in the United States. Prostate-specific membrane antigen (PSMA) is a type II transmembrane protein that acts as a glutamate carboxypeptidase enzyme. Its' high expression in prostate cancer cells makes it a useful target for diagnostic and therapeutic applications in nuclear medicine. One of the most common indications for Ga68 PSMA PET/CT is biochemical failure in castrate resistant prostate cancer (CRPC). Recent studies aimed to investigate the value of Ga68 PSMA PET/CT in patients (pts) with biochemical failure have shown a detection rate of up to 97% with good correlation to PSA levels and PSA velocity. The aim of the study was to investigate the characteristics of CRPC pts with biochemical failure and negative Ga68-PSMA in comparison to those with positive studies. Materials and methods: All Ga68-PSMA studies performed for the indication of CRPC with biochemical failure in two academic centers over a period of 24 months were retrospectively reviewed. Clinical, laboratory and imaging data including: demographic data, Gleason score at diagnosis, PSA levels and treatment history, were collected and analyzed. The different characteristics of pts with negative Ga68 PSMA PET/CT were compared to those with positive studies. Differences between groups were analyzed using student t-test, p<0.05 was considered statistically significant.
Results: Two hundred and seventy studies were performed in 266 prostate cancer pts with biochemical failure. There were 181 (67%) positive studies (in 178 pts) and 89 (33%) studies in 88 pts were negative. The mean age of the pts with positive studies was 65.7 years (48-82y) and of those with negative studies was 62.8 years (48-79y). The mean Gleason score at diagnosis was 7.5 (5-10) for the positive studies and 7 (6-9) for the negative group (p=0.006).The average PSA level at the time of the study was 20.5 ng/mL (0.12-416 ng/mL) in the positive group and 3.6 ng/mL (0.02-75 ng/mL) in pts with negative PET/CT results (p=0.002). The treatment history of the PET/CT positive group included radical prostatectomy in 65 pts (37%), hormonal therapy (109 pts, 60%), local radiotherapy (109 pts, 60%) and other treatments (including brachytherapy, radiotherapy to other body parts apart from the pelvis, therapy with radioactive drugs and chemotherapy) in 31 pts (17%). Fifty-three (60%) of the pts with negative PET/CT studies underwent radical prostatectomy, 33 (37%) received hormonal therapy, 42 (48%) had radiotherapy to the pelvis and 4 (4%) had brachytherapy. Previous radical prostatectomy was more prevalent in pts with negative studies in comparison to those with positive results (60% vs. 37%) (p=0.0025). Overall, pts with positive studies underwent more treatment regimens per patient in comparison to the group of pts with negative PET/CT results (1.76 vs. 1.48) (p=0.034).
Conclusions: Ga68-PSMA PET/CT was negative in one third of CRPC pts with biochemical failure. Positive studies were associated with greater Gleason scores at diagnosis and higher PSA values. Previous radical prostatectomy was more common in pts with biochemical failure and negative studies , however, pts with positive studies underwent more treatment regimens in comparison to pts with negative PET/CT studies.