Prostate cancer with low burden skeletal disease at diagnosis: outcome of concomitant radiotherapy on primary tumor and metastases.

Objective: To evaluate toxicity and clinical outcome in synchronous bone only oligometastatic (5.2 lesions) prostate cancer patients, simultaneously irradiated to prostate/prostatic bed, lymph nodes and bone metastases. Methods: From 2/2009 to 6/2015, 39 bone only prostate cancer patients underwent radiotherapy (RT) at "radical" doses to bone metastases (median 2 Gy equivalent dose, EG1D2>40Gy, alpha/beta = 1,5), nodes, and prostate/ prostatic bed, within the same RT course, in association with androgen deprivation therapy (ADT). Biochemical relapse-free survival, clinical relapse-free survival, freedom from distant metastases and overall survival were evaluated. Results: After a median follow-up of 46.5 (1.2-103.6) months, S patients died from disease progression, 10 experienced biochemical relapse, 19, still in ADT, presented undetectable prostate-specific antigen (PSA) at the last follow-up. Five patients who discontinued ADT after a median of 34 months (5.8-41) are free from biochemical relapse. The 4 year Kaplan-Meier estimates of biochemical relapse-free survival, clinical relapse-free survival, freedom from distant metastases and overall survival were 53.3%, 65.7%, 73.4% and 82.4% respectively. No Grade > 2 acute events and only two severe late urinary events were recorded, not due to the concomitant treatment of primary and metastatic disease. Conclusion: Our results suggest that "radical" and synchronous irradiation of primitive tumor and metastatic disease may be a valid approach in synchronous bone only prostate cancer patients, showing mild toxicity profile and promising survival results. Advances in knowledge: To the best of our knowledge, this is the first analysis of clinical outcome in synchronous bone-only metastasis (neither nodal nor visceral) patients at diagnosis, treated with radical RT to all disease, associated to ADT.