Addition of PSMA PET led to notable stage migration in mHSPC, study shows

Findings from a recent study published in the Journal of Nuclear Medicine suggest that the addition of prostate-specific membrane antigen (PSMA) PET imaging to conventional imaging-based assessments may lead to significant stage migration in patients with metastatic hormone-sensitive prostate cancer (mHSPC).¹

In total, 22% of patients migrated from low-volume disease on conventional imaging to high-volume disease on PSMA PET.

The authors explained, “High-volume disease and low-volume disease definitions in mHSPC patients are based on conventional imaging (CT/MRI with bone scan) according to CHAARTED criteria. [High-volume disease] and [low-volume disease] definitions are associated with overall survival and are used for treatment decisions. It remains unknown how these definitions transfer to PSMA PET imaging.”

In total, the study retrospectively assessed 67 patients with mHSPC who underwent imaging across 5 international sites. All patients received PSMA PET/CT or PSMA PET/MRI and bone scan within 100 days and without the initiation of a new therapy between the 2 scans.

According to the authors, “[High-volume disease] was defined by the presence of visceral metastases or at least 4 bone metastases (with ≥1 beyond the spine or pelvis).”

Based on these criteria, 25.4% of patients (17 of 67) had high-volume disease and 74.6% of patients (50 of 67) had low-volume disease on conventional imaging. On PSMA PET, 40.3% of patients (27 of 67) had high-volume disease and 35.8% of patients (24 of 67) had low-volume disease. Additionally, 22.4% of patients had no visible lesion or only locoregional pelvic disease (M0) on PSMA PET imaging.

In total, 40.3% of patients experienced a change in staging between initial assessment on conventional imaging and PSMA PET. This included 22% of patients (11 of 50) who migrated from low-volume disease on conventional imaging to high-volume disease on PSMA PET. Additionally, 5.9% of patients (1 of 17) classified as high-volume disease and 30% of patients (15 of 50) classified as low-volume disease on conventional imaging migrated to M0 staging on PSMA PET.

The investigators then assessed whole-body tumor burden by automated bone scan index (aBSI) on bone scan and whole body PSMA PET-positive tumor volume (PSMA PET-TV) on PSMA PET.

Patients with high-volume disease on conventional imaging had a median whole body PSMA-TV of 248.0 mL and a median aBSI of 3.4%. For those with low-volume disease on conventional imaging, the median whole body PSMA-TV was 25.1 mL, and the median aBSI was 0.1%.

Further, for patients classified at high-volume disease on PSMA-PET, the median whole-body PSMA-TV was 141.0 mL and the median aBSI was 0.9%. The median whole-body PSMA-TV and aBSI for patients classified as low-volume disease on PSMA PET was 31.5 mL and 0%, respectively.

The authors also noted that the optimal whole-body PSMA-TV to stratify low-volume vs high-volume disease on conventional imaging using CHAARTED criteria was determined to be 107 mL. However, this led to a misclassification rate of 21.9%.

The authors concluded, “Compared with [conventional imaging], addition of PSMA PET leads to M0 downstaging in every third and [low-volume disease] to [high-volume disease] upstaging in every fifth mHSPC patient. Future [high-volume disease] and [low-volume disease] definitions based on PSMA PET/CT should be adjusted based on patient outcome.”

Reference

1. Unterrainer LM, Hope TA, Fendler WP, et al. Low- and high-volume disease in metastatic hormone-sensitive prostate cancer: From CHAARTED to PSMA PET-An international multicenter retrospective study. J Nucl Med. 2025;66(1):54-60. doi:10.2967/jnumed.124.268441