(UroToday.com) The 2024 American Society of Clinical Oncology (ASCO) Annual Meeting held in Chicago, IL between May 31st and June 4th, 2024 was host to a prostate, testicular, and penile cancers poster session. Dr. Emilio Giunta presented the results of a prospective study evaluating the association between 68Ga-PSMA PET/CT response and clinical outcomes in metastatic castrate-resistant prostate cancer (mCRPC) patients treated with first-line enzalutamide.
There has been a long-standing interest in evaluating 68Ga-PSMA PET/CT as a response assessment tool for mCRPC patients receiving systemic therapy. In this study, the investigators evaluated the impact of 68Ga-PSMA PET/CT response, as compared to prostate-specific antigen (PSA) response, in patients treated with enzalutamide as first-line therapy for mCRPC.
This was a prospective observational study of 70 consecutive mCRPC patients treated with 1st line enzalutamide 160 mg once daily and who underwent a 68Ga-PSMA PET/CT within three weeks before (baseline) and 12 weeks after (SD: ±4 weeks) treatment initiation, between October 2017 and May 2022.
The investigators assessed the following parameters at both time points:
- Sum of metabolic total volume (sMTV)
- Mean and maximum standardized uptake volume (sSUVmean and sSUVmax, respectively)
- Total lesion activity, which is the product of MTV and SUVmean, for a maximum of 20 lesions
Using the EAU/EANM criteria, patients were categorized as PSMA responders (PET-R, in case of complete/partial response or stable disease) or PSMA non-responders (PET-NR, in case
of progressive disease). Based on the serum prostate-specific antigen (PSA) levels, patients were
classified as biochemical responders (PSA-R, in case of PSA decrease ≥ 50%) or non-responders
(PSA-NR in all other cases). Survival analyses were performed using the Cox regression hazard model and the Kaplan-Meier method.
At the data cut-off date of December 2023, 69 mCRPC patients were fully evaluable. The median follow-up was 57 months (range: 3–74). The baseline patient characteristics are summarized below. The median age was 75 years. The median baseline PSA level was 2.57 ng/ml. The most common site of PSMA-PET visible disease was lymph nodes (67%), followed by bone (54%) and prostate (36%).
The median progression-free survival (PFS) was 36.7 months (95% CI: 26.4–66.5), while the median overall survival (OS) was 66.5 months (95% CI: 38.3–not reached). A contingency table summarizing the concordance/discordance between PSA and PSMA PET responses after three months of starting enzalutamide is illustrated below.
Differences between the discordant groups (PSA-R/PET-NR and PSA-NR/PET-R) were not statistically significant for both median progression-free survival (mPFS) and median overall survival (mOS) (p=0.09 and 0.41, respectively), even if a positive trend for PSMA PET was shown (Table 2).
On multivariable analysis, only total lesion activity at 12 weeks was significantly associated with both median PFS and median OS (Table 3).
Dr. Giunta concluded as follows:
- PSA monitoring is less informative than 68Ga-PSMA PET/CT response to predict progression-free survival in mCRPC patients receiving enzalutamide as first-line therapy.
- Some PET parameters may better predict survival benefit but need future validation.
Presented by: Emilio Francesco Giunta, MD, Department of Medical Oncology, IRCCS Istituto Romagnolo per lo Studio dei Tumori (IRST) "Dino Amadori", Meldola, Italy.
Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, May 31st – June 4th, 2024