Radiotherapy in metastatic castration resistant prostate cancer patients with oligo-progression during abiraterone-enzalutamide treatment: a mono-institutional experience.

Background: Some patients experience oligo-progression during androgen receptor targeted therapy (ARTT) treatments. This progression might not indicate a real systemic drug resistance, but a selective monoclonal resistance. With the aim to delay the start of new line treatments we treated oligo-progressive sites with radiotherapy.
Methods: From June 2011 to Febrary 2019, 29 consecutive metastatic castration resistant prostate cancer (mCRPC) patients were submitted to radiotherapy for oligo-progression (1-3 sites) during ARTT for a total of 37 lesions treated. Thirty-one (83.8%) lesions were treated with conformal radiotherapy and 6 (16.2%) with stereotactic radiotherapy. After radiotherapy all patients continued ARTT.
Results: Median OS (calculated from ARTT start) was 46,6 months (range 4.4-97.5 months), 2 and 3-year OS were 82.8 and 70.7%, respectively. Median PFS was 18,4 months (range 4.4-45.3 months), 2 and 3-year PFS were 38.3 and 8.5%, respectively. Median overall duration of ARTT treatment was 14.8 months (range 4.4-45.3 months) and median duration of ARTT after radiotherapy was 4.6 months (range 1-33.8 months). Patients submitted to radiotherapy > 6 months from the start of ARTT presented a better PFS (p < 0.001) and a trend toward a better OS (p = 0.101). None patient presented RT and drug related toxicities.
Conclusions: Radiotherapy of oligoprogressive sites may prolong the duration of disease control under ARTT in mCRPC patients with a possible delay in the start of new line treatment. Patients progressing within 6 months from the start of ARTT did not benefit from this approach. More studies are necessary to confirm our results and to evaluate other prognostic factor in order to select patients with high benefit from this approach.