Oncological Outcomes in Patients with Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography-detected Oligometastatic Prostate Cancer Treated with Metastasis-directed Radiotherapy as the Single Treatment Modality.

[BACKGROUND AND OBJECTIVE] In patients with biochemical recurrence (BCR), prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) can detect oligometastatic prostate cancer (PCa). However, the optimal treatment approach for oligometastatic disease remains unclear. This study aims to assess the oncological outcomes of metachronous oligometastatic PCa patients treated with metastasis-directed radiotherapy (MDRT).

[METHODS] We retrospectively evaluated patients with hormone-sensitive, metachronous oligometastatic PCa who underwent MDRT for BCR (from July 2012 to September 2022). Patients had one to four lymph nodes and/or bone metastases on PSMA PET/CT and were irradiated with 5 × 7 or 3 × 10 Gy. The biochemical response to MDRT was assessed as undetectable prostate-specific antigen (PSA) at follow-up, PSA response (PSA ≤ pretreatment level), or biochemical progression (PSA > pretreatment level). Biochemical progression-free survival (bPFS) and local remission of disease (absence of disease at the MDRT site on follow-up PSMA PET/CT or undetectable PSA) were evaluated.

[KEY FINDINGS AND LIMITATIONS] Eighty patients underwent MDRT for 105 PSMA PET/CT-confirmed lesions. The median time from curative treatment to MDRT was 55 mo (interquartile range [IQR] 31-103). At a median follow-up of 32 mo after MDRT (IQR 21-64), 10% of the patients were PSA free, 10% had a PSA response, and 80% experienced biochemical progression. The bPFS rates at 1 and 2 yr were 54% and 38%, respectively. A total of 87% of patients had local control of disease after MDRT, whereas 72% had new metastatic lesions on repeated PSMA PET/CT. Limitations include the retrospective design and a small cohort.

[CONCLUSIONS AND CLINICAL IMPLICATIONS] MDRT for oligometastatic disease shows high local efficacy. However, disease progression is observed in a substantial proportion of patients.