(UroToday.com) The 2023 European Society of Medical Oncology (ESMO) Annual Congress held in Madrid, Spain between October 20th and 24th, 2023 was host to a prostate cancer abstracts poster session. Dr. Lena Unterrainer presented the results of an analysis evaluating the impact of prostate-specific membrane antigen positron emission tomography (PSMA PET) scans for ‘upstaging’ or ‘downstaging’ patients with metastatic hormone sensitive prostate cancer (mHSPC), using the CHAARTED criteria.
The CHAARTED definition for low- and high-volume disease currently relies on conventional imaging. This definition has been used to guide treatment decisions in the metastatic hormone-sensitive disease space and is associated with overall survival outcomes. The increased uptake of PSMA PET scans has led to an observed stage migration phenomenon and, as such, it remains unknown whether the conventional imaging-defined criteria for high/low volume disease can be transferred to PSMA PET imaging.
The volume of disease (high-volume disease / low-volume disease) as defined by the CHAARTED criteria based on conventional imaging, is associated with overall survival and used for guiding treatment decisions in mHSPC patients. It remains unknown how the definition of high and low volume disease can be transferred to PSMA PET imaging.
This was a retrospective study across four international sites of mHSPC patients who underwent a (68Ga-PSMA-11 PET/CT or PET/MRI) + bone scan within 100 days of study inclusion. Patients who were treated in the interval between both scans were excluded. The bone scan and CT or MRI component of the PET/CT or PET/MRI were used as the conventional imaging tools, and high/low-volume CHAARTED stratification criteria using these imaging tools were initially applied. These criteria were subsequently applied to the PSMA PET scans. High-volume disease was defined by the presence of visceral metastases and/or > 4 bone metastases (with > 1 beyond spine and pelvis). EXINIboneTM 3.4 (EXINI Diagnostics) was used for ascertaining the number/localization of bone metastases on bone scan. The whole-body PSMA PET positive tumor volume (PSMA-TV) was obtained using a semi-automatic thresholding method on Affinity 3.0.2 (Hermes Medical Solutions).
The study cohort included 50 mHSPC patients with paired PSMA PET + bone scans. The median PSA was 43.8 ng/ml.
Conventional imaging findings were as follows:
- Disease in prostatic fossa: 13/50
- Lymph nodes: 25/50
- Bones: 34/50
- Visceral organs: 2/50
PSMA PET findings were as follows:
- Prostatic fossa disease: 31/50
- Lymph nodes: 28/50
- Bones: 29/50
- Visceral organs: 2/50
Based on conventional imaging, 27% of patients had high-volume disease (remaining low volume). Conversely, when the criteria were applied to PSMA PET findings, 42% of patients were stratified into the high-volume category (low volume: 44%). 7/50 (14%) patients had no PSMA-positive lesion or disease limited to the prostate fossa (all were low-volume disease on conventional imaging).
Overall, the mean whole body PSMA-TV was 248.1 ml (range: 0 – 3734.0 ml). In conventional imaging defined high-volume disease, the mean whole body PSMA-TV was 713.7 (0.3 – 3734.0) ml, compared to 46.4 (0-228.0) ml for conventional imaging low-volume disease.
Downstaging from conventional imaging to PSMA-PET occurred in in 7/50 patients (14%), whereas upstaging (low to high volume) was observed in 8/50 patients (16%).
Dr. Unterrainer concluded that stage migration between low- and high-volume disease from conventional imaging to PSMA PET occurs both by up- and downstaging. Correlation with outcomes will lead to new definitions of high- and low-volume disease based on PSMA PET/CT.
Presented by: Lena Unterrainer, MD, Ahmanson Translational Theranostics Division, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, UCLA, Los Angeles, CA
Written by: Rashid K. Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 European Society of Medical Oncology (ESMO) Annual Congress held in Madrid, Spain between October 20th and 24th, 2023