Abstract
BackgroundProstate-specific membrane antigen (PSMA) targeting radioligands have transformed treatment of prostate cancer. Radioligand therapy (RLT) with 177Lu-PSMA in metastasized castration resistant prostate cancer (mCRPC) achieves objective response and disease stabilization in roughly two third of patients, whereas one third of patients progress. This study was performed to assess the role of interim PSMA PET/CT after the 2nd cycle of RLT for early prediction of overall survival in patients undergoing RLT with 177Lu-PSMA.Methods38 mCRPC patients (68.9 ± 8.1 y) treated with at least two cycles of RLT at 8 week intervals and interim 68Ga-PSMA PET/CT (PET) at 8–10 weeks after the 2nd cycle of RLT were included in this study. Prostate-specific antigen (PSA) response was evaluated according to the Prostate Cancer Working Group 3 criteria. Radiographic response assessment of soft tissue, lymph node, and bone lesions was performed according to RECIST 1.1 including the PET component. Patients’ data were collected for follow-up from the local Comprehensive Cancer Center Register.ResultsMedian follow-up was 19.7 months (4.7–45.3). PSA response after the 2nd therapy cycle showed partial remission (PR) in 23.7%, stable disease (SD) in 50%, and progressive disease (PD) in 26.3% of patients. In comparison, 52.6, 23.7, and 23.7% of patients showed PR, SD, and PD respectively on PET/CT. The strength of agreement between PSA response and PET/CT response criteria was only fair (kappa 0.346). Median overall survival (OS) was 22.5 months (95% CI: 15.8–29.2). Median OS stratified to PSA/PET response was 25.6/25.6 months for PR, 21.7/30.6 months for SD and 19.4/13.1 months for PD (p = 0.496 for PSA and 0.013 for PET/CT response).ConclusionsInterim PSMA PET/CT based response evaluation at 8–10 weeks after the 2nd cycle of RLT is predictive of overall survival and PD in patients treated with 177Lu-PSMA. On the contrary, PSA appears to have only limited predictive value.
Highlights
Prostate cancer (PCa) is one of the most common cancers and the second most frequent cause of cancer related mortality in the United States [1]
Patients (n = 38) who were investigated with interim Prostate specific membrane antigen (PSMA) PET/CT after two therapy cycles were included for the analyses
radioligand therapy (RLT) with 177LuPSMA and imaging with 68Ga-PSMA were both performed under national regulations of compassionate use of a nonapproved drug according to AMG §13.2b (German Medicinal Product §13.2b) [14, 15]
Summary
Prostate cancer (PCa) is one of the most common cancers and the second most frequent cause of cancer related mortality in the United States [1]. Despite advancement in the therapeutic armamentarium, the 5-year survival rate is approximately three times higher in patients with locally advanced PCa in comparison to metastasized PCa [1]. This highlights the need for development of novel treatment options and improvement of existing ones for metastasized PCa. In addition, considering the number of different treatment options and their toxicity, standardization of the sequences of treatment regimens and defining subgroups of patients with poor outcomes upfront are an absolute necessity. Prostate specific membrane antigen (PSMA) is over-expressed in PCa, both on the primary tumor as well as in metastases [2]. Prostate-specific membrane antigen (PSMA) targeting radioligands have transformed treatment of prostate cancer. This study was performed to assess the role of interim PSMA PET/CT after the 2nd cycle of RLT for early prediction of overall survival in patients undergoing RLT with 177Lu-PSMA
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