Clinical impact of PSMA PET in patients with biochemically recurrent prostate cancer after locoregional definitive therapy.

Abstract

e17009 Background: [68Ga]-PSMA-11 positron emission tomography (PSMA PET) detects sites of biochemically recurrent prostate cancer (BCR) at higher rates than conventional imaging. We hypothesized that PSMA PET would lead to high change in management (CIM) rates in this setting. Methods: We prospectively recruited patients (pts) with BCR, defined as confirmed PSA > 0.2 ng/mL > 6 weeks post-surgery or PSA ≥2 ng/mL above nadir post-radiation therapy, to undergo Ga-68 PSMA-11 PET. Some also had equivocal lesions on CT, MRI, bone scan, or fluciclovine PET obtained prior to PSMA PET. Pre-PET intended treatment, PSA (ng/mL), and PSA doubling time (PSAdt, months) from most recent 3 values were recorded prior to imaging. Post-PET treatment (intended or actual) was collected from medical record. CIM was categorized as major (change in or addition of treatment modality) vs minor (change within treatment modality, such as altered radiation field). Any lesion with uptake above blood pool was interpreted as positive for prostate cancer by an experienced PET reader (DLC). All values were represented as the median [interquartile range, IQR]. Kruskal Wallis analysis tested for significant differences among groups. Results: 44 pts with BCR age 71 [10] with Gleason scores (GS) at diagnosis of 6 (N = 2), 7 (N = 23), 8 (N = 5), and 9 (N = 13) enrolled, 14/44 with equivocal lesions on conventional imaging. 42 had post-PSMA PET treatment decisions available in medical records for CIM analysis. Time from PSA nadir to PSA at time of PSMA PET was 5 [7.25] months. PSMA PET was positive in 33 (8/33 with equivocal lesions on prior imaging; 7 local disease only; 11 regional nodal metastases, 2/11 also with local disease; and 15 with distant metastases, 4/15 also with local disease, 9/15 with regional nodal metastases), negative in 6, and equivocal in 5 pts. Of those with distant metastases, 8 had oligometastases, defined as 3 or fewer distinct sites (1 site = single nodal region or single bone lesion), 4 in bones and 4 in distant nodes. CIM rate was 71% (30/42) overall, 65.5% (16/29 major, 3/29 minor) in pts with BCR and negative conventional imaging; 84.6% (11/13, all major) in pts with equivocal lesions on conventional imaging. Of the patients with major CIM, a treatment modality was added in 21/27, modality switched in 3/27, and a modality removed in 3/27. PSA was significantly lower (p = 0.04) for those with negative or equivocal PSMA PET (0.5 [2.7]) than those with localized disease (4.1 [2.8]), regional nodal (1.1 [3.4]) or distant metastases (3.8 [5.3]), but not PSAdt (p = 0.2, negative/equivocal PET 5 [6.5], localized 15 [36], regional nodal metastases 11 [13], distant metastases 6 [6]). Conclusions: PSMA PET may impact decision making in pts with BCR after treatment of localized prostate cancer, particularly for those with equivocal findings on conventional imaging, regardless of clinical risk at diagnosis. Clinical trial information: NCT04777071.