RT Journal Article
SR Electronic
T1 <em><sup>68</sup></em><em>Ga-PSMA PET/CT for response assessment and outcome prediction in metastatic prostate cancer undergoing taxane-based chemotherapy</em>
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 15
OP 15
VO 62
IS supplement 1
A1 Qaid Shagera
A1 Carlos Artigas
A1 Spyridon Sideris
A1 Nieves Martinez Chanza
A1 Thierry Gil
A1 Alexandre Peltier
A1 Patrick Flamen
YR 2021
UL http://jnm.snmjournals.org/content/62/supplement_1/15.abstract
AB 15Purpose: 68Ga-PSMA PET/CT is the most accurate imaging technique to detect metastatic prostate cancer (mPCa), mainly at biochemical relapse. However, its role in response assessment is not thoroughly investigated. Therefore, we aimed to evaluate 68Ga-PSMA PET/CT's role for response assessment in mPCa patients undergoing taxane-based chemotherapy and its relationship with patient outcomes. Methods: We retrospectively enrolled patients with metastatic hormone-sensitive and castration-resistant prostate cancer (mHSPC and mCRPC) who underwent a 68Ga-PSMA PET/CT scan within one month before and up to 3 months after docetaxel or cabazitaxel treatment with no therapy modification between the scans. The biochemical response (BR) was defined as a decrease of the prostate-specific antigen (PSA) level by ≥50% from the baseline. Prostate-specific membrane antigen (PSMA) expression changes on PET/CT were measured using whole-body PSMA tumor volume (PSMA-TV), using the fixed SUV=3 method. The response was assessed on a per-patient basis. Inspired by the consensus statement on PSMA PET/CT response criteria[1], patients were classified as PSMA-PET non-responders (PET-NR), including patients with ≥2 new lesions or increase of PSMA-TV by ≥30% (progressive disease, PD) or PSMA-TV change between ±29% (stable disease, SD) and PSMA-PET responders (PET-R), including patients with the disappearance of all PET-positive lesions (complete response, CR), or a decrease of PSMA-TV by ≥30% (partial response, PR). The correlation between the PSMA-PET response and BR was evaluated. Cox regression analyses and Kaplan-Meier curves were used to assess the relationship between PSMA-PET response criteria and patient outcomes (PFS and OS) as defined by PCWG3 criteria. Multivariate analysis was performed, looking for possible confounding factors for our results. Results: A total of 37 patients fulfilled the inclusion criteria (8 mHSPC and 29 mCRPC). Twenty-one patients received docetaxel, and 16 received cabazitaxel therapy (median, 6 cycles). BR was found in 18 patients and biochemical non-response (BNR) in 19 patients. Based on PET/CT, 19 patients were PET-R (6 CR and 13 PR) and 18 PET-NR (17 PD and 2 SD). PSA-based response and PSMA PET/CT based response were concordant in 95% of patients, with 18 patients BNR/PET-NR and 17 BR/PET-R (Phi = 0.89, p&lt;0.0001). One patient was BNR/PET-R with PSA increased by 96%, but PSMA-TV decreased by 42%, and one patient BR/PET-NR with PSA decreased by 52%, but &gt;2 new lesions found on PSMA PET/CT. The median follow-up was 20 months with statistically significant shorter PFS in PET-NR compared to PET-R patients (median PFS: 5.4 months vs. 13 months, respectively, HR 3.64, 95% CI 2.22—5.95, p&lt;0.0001) and worse overall survival (OS) with 58% 12-month and 42% 24-month OS compared to 100% 12-month and 94% 24-month OS, respectively (HR 4.64, 95% CI 1.86—11.58, p=0.001). The PSMA-PET response criteria adjusted to baseline risk factors, including disease stage (mHSPC vs. mCRPC), PSA level, hemoglobin and alkaline phosphatase in two multivariate models analyses. The PSMA-PET/CT based response retained significance for PFS and OS (P&lt;0.05). Conclusions: This retrospective analysis suggests that PSMA PET/CT is a promising imaging tool to evaluate the response to taxane-based chemotherapy in mPCa. PSMA-expression changes are highly concordant with PSA changes and independently associated with patient outcomes with a statistically significant difference in PFS and OS between PET-R and PET-NR patients. A prospective study is planned at our institution to confirm these results Keywords: PSMA PET/CT, prostate cancer, response, chemotherapy [1] Fanti S, et al. Eur J Nucl Med Mol Imaging. 2020;10.1007/s00259-020-04934-4.