Low- and high-volume disease in mHSPC, from CHAARTED to PSMA-PET: An international multicenter retrospective study.

Abstract

44 Background: High-volume disease (HVD) and low-volume disease (LVD) definitions are based on conventional imaging (CI = CT + bone scan (BS)) according to CHAARTED. Volume of disease is associated with overall survival and used for treatment decisions in mHSPC patients. It remains unknown how these definitions transfer to PSMA-PET. Methods: mHSPC patients from 4 international sites who underwent PSMA-PET+BS within a maximum time interval of 100 days and without any new treatment in between were retrospectively included. CHAARTED stratification into HVD/LVD was applied to BS, CT, MRI and PSMA-PET. HVD was defined by the presence of visceral metastases and/or ≥ 4 bone metastases (with ≥ 1 beyond spine / pelvis). EXINIbone 3.4 (EXINI Diagnostics) was used for the automated bone scan index (aBSI) and the number/localization of lesions on BS. The whole-body (WB) PSMA-PET positive tumor volume (PSMA-TV) was obtained using a semi-automatic thresholding method on Affinity 3.0.2 (Hermes Medical Solutions). Results: Fifty-sevenpairs of PSMA-PET/CT+BS were included (median PSA 226.0 (0.2–2840.0 ng/ml). Based on CI, 16/57 patients had CI-HVD (28.1%) and 41/57 CI-LVD (71.9%). Based on PSMA-PET, 25/57 patients had PSMA-HVD (43.9%) and 19/57 PSMA-LVD (33.3%), 13/57 (22.8%) patients had on PSMA-PET no PSMA-positive or only local / N1-disease. Upshift and downshift from CI to PSMA-PET occurred in 22/57 (38.6%): 9/57 (22.0%) patients were upstaged and 13/57 (22.8%) were downstaged by PSMA-PET. The downshifted patients had no PSMA-PET-positive lesion or only in the prostate fossa while CI was M1 disease. The mean WB-PSMA-TV and aBSI were for CI-HVD was 778.2 ml (0.3–3734.0) and 3.8% (0–11.7), for CI-LVD 51.6 ml (0–228.0) and 0.1% (0–0.6), for PSMA-HVD 573.7 ml (7.9–3734.0) and 2.6% (0–11.7) and for PSMA-LVD, 49.4 ml (1.6–228.0) and 0.1% (0–0.6), respectively. Conclusions: Stage migration between LVD and HVD from CI to PSMA-PET occurs both by up- and downstaging. HVD/LVD based on PSMA PET/CT should be redefined based on patients’ outcome.