PSMA PET/CT has shown greater sensitivity for detection of prostate cancer metastases compared to conventional imaging. Studies using PSMA PET/CT at biochemical recurrence have focused on detecting oligometastatic disease potentially amenable to surgical resection or stereotactic ablative body radiotherapy. The role of PSMA PET/CT in assessing response to systemic therapy is unknown. We examined PSMA PET/CT responses in a cohort of mPC pts who received upfront chemohormonal therapy.
Clinical and PSMA PET/CT data were retrospectively collected from two sites in Melbourne, Australia. mPC pts were eligible for inclusion if they received upfront chemohormonal therapy and underwent PSMA PET/CT imaging at baseline and within 8 weeks of completing docetaxel. Descriptive statistics correlated PSMA PET/CT response with PSA ≤ 0.2ng/mL and development of castration-resistant prostate cancer (CRPC) at 12 months (mo).
We identified 28 eligible mPC pts. 8 (29%) had de novo mPC, 19 (68%) had prior prostatectomy and 1 (3%) had prior radical radiotherapy. 54% (n = 15) had high volume metastatic burden as defined by CHAARTED. Median PSA at baseline was 10.8 (range 0.13 - 700). All pts completed 6 cycles of docetaxel. Following docetaxel, median PSA was 0.17 (range < 0.01 - 7.9), with 14 (50%) achieving PSA ≤ 0.2. Post chemotherapy PSMA PET/CT demonstrated reduced metastatic burden in all pts, with complete response (CR) in 10 pts (36%) and residual oligometastatic disease (<5 metastases) in 12 pts (43%). 80% of pts with PSMA PET/CT CR also had PSA ≤ 0.2. 22 pts (64%) had at least 12 mo follow up with 5 (23%) developing CRPC in that time: At 12 mo, CRPC developed in 8% (1/12) of those achieving PSA ≤ 0.2, 22% (2/9) of those achieving PSMA PET CR, and 13% (1/8) of those with residual oligometastatic disease.
In our small cohort of mPC pts completing upfront docetaxel, CR on PSMA PET/CT correlated strongly with PSA ≤ 0.2, a known good prognostic marker. The use of PSMA PET/CT in assessing response to systemic treatment requires further evaluation.
Clinical trial identification
Legal entity responsible for the study
Walter and Eliza Hall Institute.
Has not received any funding.
All authors have declared no conflicts of interest.