Performance and impact on management of Ga68 PSAM11 staging PET/Ct in patients with Gleason 6 and 7 prostate cancer

Introduction: While there is ample evidence about the clinical usefulness of staging high risk prostate cancer (Gleason≥ 8 and /or PSA>20) with Ga⁶⁸-PSMA PET/CT there is little data about its performance in low risk disease ( Gleason 6 PSA< 10) and insufficient information about staging intermediate risk disease ( Gleason 7, 10 < PSA< 20)

Objective: Measure the performance and impact on management of Ga⁶⁸ PSMA-11 PET/CT in low and intermediate risk disease

Methods: Retrospective review of results of PET PSMA in a single institution from January 2018 to November 2022. Gold standard was outcome and survival of low grade disease and surgical findings in intermediate risk disease for the patients who underwent surgery. Only patients who did undergo CT and bone scan prior to staging PET/CT were included

Results: There were 37 staging studies in patients with Gleason 6 and PSA< 10. The primary was not clearly seen in 16 / 37 (43.2%) and in only one patient (2.7%) was there evidence for disease outside the prostate (pelvic LN).The patient underwent appropriate treatment. The other 36 were placed under observation and are still alive (Follow up 6-46 months Mean 26 months) with a stable PSA.

There were 332 staging PET studies in Gleason 7 patients with 10< PSA<20 (265pts (3+4) (group a) and 67 (4+ 3) (group b).

In groups a and b, all primaries were clearly identified by PET as compared to biopsy data

In group a avid pelvic LNs only were identified in 32 (12.1%) and distant disease in 28 (9.6%) Management was changed in 38 patients from local (Surgery or EBRT) to systemic treatment (14.3%)

In group b avid pelvic LNs only were identified in 21 (31.3%) and distant disease in 16 (23.8%).Management was changed in 24 patients (35.8%) from local to systemic treatment

Of the 227 patients in group a and the 43 patients in group b eligible for local treatment 130 in group a and 20 in group b underwent surgery which confirmed the presence of disease in 98% of positive LNs on PET while finding many more LNs with microscopic disease (Sens 43%)

The incidence of avid pelvic lymph nodes was significantly higher in Gleason 7 (4+3) than in Gleason 7(3+4)( p<0.001) and the incidence of distant disease was higher in Gleason 7 (4+3) than in Gleason 7(3+4) (p=0.004) resulting in a significantly higher impact on management (p<0.001 )

Conclusions: 1. Staging PET/CT in patients with Gleason 6 and PSA< 10 may not be indicated.2.Patients with Gleason 7 (4+3) should be placed in the high risk category. 3 Our data support the use of staging PET/CT in Gleason 7 (3+4) patients with 10 >PSA>20 but more studies may be needed