1789P - Low- and high-volume disease in mHSPC: From CHAARTED to PSMA PET

Background

The volume of disease (high-volume disease (HVD) / low-volume disease (LVD)) as defined by the CHAARTED criteria based on conventional imaging, is associated with overall survival and used for treatment decisions in mHSPC patients. It remains unknown how the definition of HVD and LVD can be transferred to PSMA-PET imaging.

Methods

In this retrospective study that included 4 international sites, mHSPC patients who underwent a ⁶⁸Ga-PSMA-11 PET/CT or PET/MRI and a BS (CI) (within a maximum time interval of 100 days) were included. Treatment in between both scans was excluded. HVD and LVD was determined on the BS and on the CT or MRI component. CHAARTED stratification into HVD and LVD was also applied to PSMA-PET. HVD was defined by the presence of visceral metastases and / or > 4 bone metastases (with > 1 beyond spine and pelvis). EXINIbone^TM 3.4 (EXINI Diagnostics) was used for the number / localization of bone metastases 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

Paired PSMA-PET+BS of 50 mHSPC patients were included (median PSA 43.8 (0.2 – 2840.0) ng/ml). 13/50 patients had disease detected in the prostate fossa, 25/50 in lymph nodes, 34/50 in bones and 2/50 in visceral organs by CI and 31/50, 28/50, 29/50 and 2/50 by PSMA-PET, respectively. Based on CI, 14/50 patients had CI-HVD (28%) and 36/50 CI-LVD (72%). Based on PSMA-PET, 21/50 patients had PSMA-HVD (42%) and 22/50 PSMA-LVD (44%). 7/50 (14%) patients had no PSMA-positive lesion or only in the prostate fossa while CI was at least CI-LVD. Overall, mean WB-PSMA-TV was 248.1 ml (0 – 3734.0 ml). In CI-HVD, mean WB PSMA-TV was 713.7 (0.3 – 3734.0) ml, in CI-LVD, 46.4 (0-228.0) ml. In PSMA-HVD, 518.1 (0 – 3734.0) ml and in PSMA-LVD, 59.7 (0 – 228.0) ml. Downstaging from CI to PSMA-PET occurred in in 7/50 patients (14.0%), upstaging (LVD to HVD) in 8/50 patients (16.0%).

Conclusions

Stage migration between LVD and HVD from CI to PSMA PET occurs both by up- and downstaging. Correlation with outcome will lead to new definitions of HVD/LVD based on PSMA PET/CT.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

W. Fendler: Other, Research Funding: SOFIE Bioscience; Other, Other, Consultant, Speaker: Janssen; Other, Other, Constant, image review: Calyx; Other, Other, Consultant, speaker, research funding: Bayer; Other, Other, Consultant, speaker: Novartis; Other, Other, Speaker: Telix; Other, Other, speaker: GE, Eczacıbaşı Monrol. K. Herrmann: Financial Interests, Personal, Advisory Board: Bayer, Adacap/Novartis, Curium, Boston Scientific, GE Healthcare, AstraZeneca; Financial Interests, Personal, Invited Speaker: Sirtex, Siemens Healthineers, Monrol; Financial Interests, Personal, Other, Consultant: Amgen; Financial Interests, Personal, Other, DMSB: ymabs; Financial Interests, Personal, Advisory Board, Scientific Advisor: AdvanceCell; Financial Interests, Personal, Advisory Board, Advisor, Consultant: Janssen; Financial Interests, Personal, Advisory Board, Consultant: Eco1R; Financial Interests, Personal, Member of Board of Directors: Sofie Biosciences, Theragnostics, Pharma 15; Financial Interests, Personal, Ownership Interest: Sofie Biosciences; Financial Interests, Personal, Stocks/Shares: Aktis Oncology; Non-Financial Interests, Leadership Role, Chair Oncology&Theragnostics Committee: EANM. All other authors have declared no conflicts of interest.