Several guidelines have indicated that in patients with well-differentiated or moderately well-differentiated prostate cancer (PCa), a staging bone scan may be omitted. However, the guidelines recommendations have not yet been externally validated.

The aim of the study was to externally validate the available guidelines regarding the need for a staging bone scan in patients with newly diagnosed PCa. Moreover, we developed a novel risk stratification tool aimed at improving the accuracy of these guidelines.

The study included 853 consecutive patients diagnosed with PCa between January 2003 and June 2008 at a single centre. All patients underwent bone scan using technetium Tc 99m methylene diphosphonate at diagnosis.

The area under the curve (AUC) of the criteria suggested by the guidelines (European Association of Urology, American Urological Association, National Comprehensive Cancer Network, and American Joint Committee on Cancer) to perform a baseline bone scan was assessed and compared with the accuracy of a classification and regression tree (CART) including prostate-specific antigen (PSA), clinical stage, and biopsy Gleason sum as covariates.

The AUC of the guidelines ranged between 79.7% and 82.6%. However, the novel CART model, which stratified patients into low risk (biopsy Gleason ≤7, cT1-T3, and PSA <10 ng/ml), intermediate risk (biopsy Gleason ≤7, cT2/T3, and PSA >10 ng/ml), and high risk (biopsy Gleason >7) was significantly more accurate (AUC: 88.0%) than all the guidelines (all p≤0.002). The limitation of this study resides in its retrospective design. Moreover, the proposed risk stratification tool can be considered only for patients who are candidates for radical prostatectomy until validated in other clinical settings.

This is the first study aimed at externally validating the available guidelines addressing the need for staging baseline bone scans in PCa patients. All guidelines showed high accuracy. However, their accuracy was significantly lower compared with the accuracy of the novel risk stratification tool. According to this tool, staging bone scans might be considered only for patients with a biopsy Gleason score >7 or with a PSA >10 ng/ml and palpable disease (cT2/T3) prior to treatment. However, before recommending its use in clinical practice, our model needs to be externally validated.