Abstract
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Objectives: 177Lu PSMA radioligand therapy (RLT) is a promising new treatment agent for patients with metastatic castration-resistant prostate cancer (MCRPC) who did not give a response to second-line treatment and progressed. We retrospectively evaluated our therapy results for better understanding the reasons for successful and unsuccessful treatment and early relapse.
Methods: 177Lu PSMA-617 radioligand therapy (RLT) was given in 23 MCRPC patients (Mean age 64.8y, range 43-81y). 68Ga PSMA-11 PET/CT was performed in all patients 1-2 weeks prior to RLT. All patients were treated with a mean of 6 GBq 177Lu PSMA-617 in a total 62 cycles (1-4 cycles per patients). Seven patients excluded from the study due to insufficient follow-up. Therapy response was evaluated with serum total PSA and imaging findings. More than 50% decrease in PSA levels two weeks after treatment and/or decrease in SUV Max values at the metastatic sites in 68Ga PSMA-11 PET/CT is considered as a good response to therapy. Increase in PSA levels and/or detection of new metastatic sites in imaging modalities is accepted as progressive disease. Mean Gleason Score was 8.25 (range 7-9). There was local recurrence in 7 (30%), bone metastases in 20 (95%), lymph node metastases in 5 (21%) and lung metastasis in 1 (5%) patients. All patients received androgen deprivation therapy and 19 patients received chemotherapy before the RLT. Results: PSA decline was more than 50% in five (31%) patients and considered as a good response to the treatment. Two or three more cycle treatment was given these patients until there was no uptake in the tumor or metastatic sites at the 68Ga PSMA PET/CT and/or PSA is less than 0.1 ng/mL. There were 7 patients (43%) with PSA decline less than 50% after the first cycle of treatment. In four of these patients there was still uptake on primary and/or metastatic sites at 68Ga PSMA PET/CT and PSA more than 0.1 ng/mL after 2 to 3 more cycle of treatment and early reaps (in less than 6 months after completion of the last cycle of treatment) was seen 3 of these patients. Four patients (25%) did not respond the treatment. In these patients, PSA continued to rise and 68Ga PSMA uptake decreased at the metastatic sites as well as new metastatic foci had been shown at the FDG PET/CT scan.
Conclusions: 177Lu PSMA-617 RLT has been shown as an effective treatment modality with low toxicity for the patients with MCRPC. The degree of SUV Max decline at the metastatic sites on 68Ga PSMA PET/CT scan and PSA response after the first cycle of therapy are good predictors of therapy response. Due to early relapse especially in patients who partially responded to the therapy should be followed up closely and when the relapse occurs additional cycle of therapy can be given safely.