Stereotactic body radiotherapy in oligoprogressive metastatic castration-resistant prostate cancer during abiraterone or enzalutamide.

Introduction: This monocentric, single-arm, retrospective study investigated the role of stereotactic body radiotherapy in patients with metastatic castration resistant prostate cancer who experienced oligoprogression during androgen receptor targeted agents.

Methods: We retrospectively enrolled metastatic castration resistant prostate cancer patients treated with androgen receptor targeted agents between December 2016 and January 2022. All patients experienced an oligoprogression (defined as the appearance and/or the progression of ⩽5 bone or nodal or soft tissue metastases) during treatment with androgen receptor targeted agents and received stereotactic body radiotherapy upon oligoprogressive sites, preserving the androgen receptor targeted agents. Further stereotactic body radiotherapy upon new metastatic sites was permitted. Patients showing visceral metastases or receiving palliative radiotherapy were excluded. Progressive disease at >5 metastatic sites or the appearance of visceral metastases led to a change of the systemic treatment. Primary endpoints were 36-month survival rate and 36-month rate of patients receiving treatment with androgen receptor targeted agents. Secondary endpoints were local disease control, biochemical response and safety.

Results: We analyzed data from 30 patients. The 36-month survival rate was 90% (27 patients); 36-month rate of patients who were still on treatment with androgen receptor targeted agents was 50%. 20 of 30 patients had performed imaging control after a single course of stereotactic body radiotherapy: overall response rate was 50%, while clinical benefit was 93%. No ⩾G2 adverse events related to stereotactic body radiotherapy were recorded.

Conclusions: Stereotactic body radiotherapy in oligoprogressive metastatic sites during androgen receptor targeted agent treatment resulted in a feasible and effective treatment to delay the start of next-line systemic treatment and prolong overall survival in metastatic castration resistant prostate cancer. Longer follow-up and further prospective studies are necessary to confirm our preliminary results.