Background: ECHOS trial is a large real-world study, which is collecting data on mCSPC patients treated in the daily clinical practice in Italy from 2015. To date, > 1500 pts were included in the study, most of them treated with DOC, according to the availability of the active agents over the time in Italy. In the present analysis, we assessed the characteristics and outcomes of mCSPC pts progressing within 6 mos from the start of DOC. Methods: We retrospectively and prospectively reviewed the clinical records of a consecutive series of mCSPC pts treated with DOC in the daily clinical practice in 69 Italian Hospitals. The treatment mostly consisted of DOC at the standard dose of 75 mg/sqm every 3 wks for six courses. For each pt we recorded the pre and post-DOC clinical history, the baseline characteristics of the pts, the treatment details and clinical outcomes. For the purpose of the present study, we considered only pts who ended chemotherapy by September 2022. PR was defined as the onset of progressive disease within 6 mos from the DOC start. Results: Among 920 mCSPC pts treated with DOC, 122 (14.3%) were PR. Most of them (95.6%) presented a de novo (DN) disease, which showed mostly high volume (HV) features (82.3%). Compared to the pts without PR, those showing PR presented more frequently a visceral involvement (26.2% vs 18.2%; p = 0.038), had lower baseline levels of hemoglobin (12.8 g/dl vs 13.4 g/dl; p < 0.0001), and higher baseline levels of lactate dehydrogenase (266 U/L vs 220,5 U/L; p < 0.002). No other significant differences were observed in terms of baseline PSA and alkaline phosphatase levels, symptoms degree, disease volume and timing of mets presentation between PR e no-PR pts. The median number of life prolonging agents administered after DOC progression was 1 in pts with PR as well as in pts without PR. The median overall survival was 11.9 mos and 44.9 mos in PR and no-PR pts, respectively (p < 0.0001). Conclusions: Our data suggest that PR led a significant worsening of prognosis with a relevant shortening of life expectancy in pts who receive DOC for mCSPC.