Low- and High-Volume Disease in Metastatic Hormone-Sensitive Prostate Cancer: From CHAARTED to PSMA PET-An...

Area of Science:

• Oncology
• Radiology
• Nuclear Medicine

Background:

• High-volume disease (HVD) and low-volume disease (LVD) in metastatic hormone-sensitive prostate cancer (mHSPC) are defined by conventional imaging (CI) and impact survival and treatment.
• The applicability of CI-based HVD/LVD definitions to prostate-specific membrane antigen (PSMA) PET imaging is not well understood.

Purpose of the Study:

• To compare CI-based disease volume criteria with PSMA PET-based volume definitions in mHSPC patients.
• To evaluate the impact of PSMA PET on disease staging compared to conventional imaging.

Main Methods:

• Retrospective multicenter study of 67 mHSPC patients who underwent both PSMA PET/CT or PET/MRI and bone scan (BS) within 100 days without new therapy.
• CHAARTED criteria for HVD/LVD were applied to CI (BS, CT, MRI) and PSMA PET.
• Whole-body tumor burden was quantified using automated bone scan index (aBSI) on BS and PSMA PET-positive tumor volume (PSMA-TV) on PSMA PET.

Main Results:

• PSMA PET identified HVD in 40.3% of patients (HVD-PET), compared to 25.4% with CI (HVD-CI).
• Stage migration occurred in 40.3% of patients: 22% of LVD-CI patients were upstaged to HVD-PET, and 30% of LVD-CI patients were downstaged to M0-PET.
• An optimal PSMA-TV threshold of 107 mL was identified to stratify LVD-CI versus HVD-CI with 21.9% misclassification.

Conclusions:

• PSMA PET imaging leads to significant stage migration in mHSPC patients compared to conventional imaging.
• M0 downstaging occurs in approximately one-third, and LVD to HVD upstaging occurs in one-fifth of patients.
• Future HVD/LVD definitions for mHSPC should be revised based on PSMA PET/CT findings and patient outcomes.