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

To evaluate toxicity and clinical outcome in synchronous bone only oligometastatic (≤2 lesions) prostate cancer patients, simultaneously irradiated to prostate/prostatic bed, lymph nodes and bone metastases. 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, EQD2>40Gy, α/β = 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. After a median follow-up of 46.5 (1.2-103.6) months, 5 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. 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. 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.