The CHAPPP study: Changing care with PSMA-PET for prostate cancer—A retrospective study of the role of PSMA imaging in altering treatment pathways.

Abstract

13 Background: The low sensitivity of standard imaging (SI) techniques in detecting metastases (Ms) may lead to unnecessary local treatment for patients (Pts) with newly diagnosed or recurrent prostate cancer (PC). Ga-68-PSMA (Prostate Specific Membrane Antigen)-PET-CT is a novel imaging technique with increased sensitivity in detection of PC especially at low PSA values and may change the decision to pursue primary local or salvage treatment. This study quantified changes in definitive local treatment secondary to occult Ms detected on Ga-68-PSMA not visualized on SI. Methods: A retrospective study was performed of 509 consecutive PSMA scans (and 481 Pts) at our tertiary cancer centre, the Royal Brisbane and Women’s Hospital between Sept 2014 and Dec 2015. PSMA imaging was compared with a CT scan and bone scan to determine whether PSMA results altered the decision to pursue local treatment. Results: 81 (16%) Pts had PSMA-PET-CT scan and no Ms on SI, 40 prior to definitive local treatment and 41 as work up for recurrence. 9/40 Pts (23%) undergoing primary work-up had PSMA-identified Ms not visible on SI and altered these patients treatment pathway (mean PSA 20.5 ng/mL). Because of PSMA-diagnosed Ms, 3 did not receive local treatment. 4 had pelvic nodal involvement and received definitive radiotherapy (RT) including nodal fields. 2 Pts proceeded to radical prostatectomy with the addition of lymph node dissection. 41 Pts investigated for recurrence following local treatment had SI for comparison, (mean PSA 4.7, range 0.11 – 35 ng/mL). 11/41 (27%) were found to have distant or nodal Ms not visualized on SI. 7/11 with prior surgery did not proceed to salvage RT and the remaining Pts who had Ms were referred for an earlier medical oncology opinion. In total 20/81 (25%) of Pts had a direct change in treatment due to the additional information conferred by PSMA imaging. Conclusions: PSMA is more sensitive in the detection of prostate cancer Ms for patients being evaluated for primary treatment or looking for recurrence following local treatment. These results show clinically meaningful changes in management with avoidance of local treatment because of enhanced detection of metastases.