Stereotactic body radiotherapy to lymph nodes in oligoprogressive castration-resistant prostate cancer patients: a post hoc analysis from two phase I clinical trials

The prognosis of prostate cancer (PC) is generally favorable but the incidence of metastases is relatively high after the treatment of the primary tumor, especially in high-risk patients. Fractionated stereotactic body radiotherapy (SBRT) or single fraction stereotactic body radiosurgery (SRS) are emerging treatment options in this setting. However, data on SBRT/SRS in patients with metastatic castration-resistant PC (mCRPC) are largely lacking, particularly in subjects with nodal lesions. Therefore, we evaluated outcomes and toxicity recorded in mCRPC patients with nodal oligoprogression. Patients included in this analysis had <= 5 metastatic sites without visceral lesions and underwent SBRT/SRS on nodal metastases. Thirty-eight patients carrying out 61 nodal metastases were analyzed. The median SRS dose was 20 Gy (range 12-24 Gy) and the most common schedule was 20 Gy (44.8%). The median SBRT dose was 45 Gy (range 20-50 Gy) and the most common regimen was 45 Gy in 5 fractions (37.9%). Thirty-seven patients (97.4%) showed only grade 0-1 acute toxicity while one patient reported grade 2 dysphagia. In terms of late toxicity, one grade 2 laryngeal, one grade 1 skin and one grade 1 gastrointestinal toxicities were recorded. Two-year actuarial local control (LC), distant progression-free survival, progression-free survival (PFS) and overall survival were 94.0, 47.2, 47.2, and 90.2%, respectively. Two-year next line systemic therapy-free survival (NEST-FS) was 67.7%. In conclusion, the efficacy in terms of LC of SBRT/SRS in patients with nodal metastases from PC was confirmed. Moreover, this analysis suggests the efficacy in terms of PFS and NEST-FS also in the setting of oligoprogressive PC. In fact, about one-third of patients were free from progressive disease and two-third of subjects did not require hormonal therapy switch or discontinuation three years after treatment.