Changing the referral criteria for bone scan in newly diagnosed prostate cancer patients

Objectives

The aim of this study was to correlate the prostate-specific antigen (PSA) level and Gleason score with staging bone scan result in patients with a new diagnosis of prostate cancer in order to establish the feasibility of implementing the European Association Urology guidelines, which state that a bone scan may not be indicated when PSA <20 in well–moderately differentiated tumours.

Methods

We identified 633 patients retrospectively and 186 patients prospectively with a new diagnosis of prostate cancer undergoing a staging bone scan between March 2005 and January 2010. Patients were excluded if there was no Gleason score available or if the PSA level was checked over 3 months prior to bone scan. Bone scan results were analysed with respect to age, PSA level and Gleason score. In the case of an equivocal result, subsequent imaging was taken into consideration or the initial bone scan was re-reviewed. In persistently equivocal cases, all relevant imaging was assessed by a blinded panel of radiologists to allow a final decision to be made.

Results

Of 672 patients aged 39–93 years (median 71 years), who fulfilled the inclusion criteria, 54 (8%) had evidence of bony metastases. PSA level and Gleason score were both independent predictors of bone scan positivity and their predictive value was additive p<0.01. None of the 357 patients with a PSA level of <20 and a Gleason score of <8 had a positive bone scan.

Conclusion

Staging bone scans in newly diagnosed prostate cancer patients with a PSA level of <20 and a Gleason score of <8 can be safely omitted, with these criteria having a negative predictive value of 100% in our series.Prostate cancer is currently the most common malignancy diagnosed in men in the UK 1] and bone is the second most common site of metastasis 2]. Bone metastases are present in up to 14% of patients at presentation 3] and in 80–85% of those who die of the disease 4], and they therefore affect morbidity, reflect prognosis and significantly influence decisions with regard to patient management.Sensitivity of planar bone scan for the detection of bone metastases is 72–77% in adults 5,6] and is currently the investigation of choice. However, it lacks diagnostic specificity, with indeterminate results often prompting the need for further imaging.Prostate-specific antigen (PSA) level is an established prognostic marker that correlates with bone scan positivity, and various studies demonstrate a low risk of a positive bone scan in newly diagnosed patients with a low PSA level 3,4,7-13]. Gleason score is also of important prognostic significance and has been shown to be an independent predictor of bone scan results on multivariate analysis 4,7,12,14]. There is still a lack of consensus, however, on the referral criteria for bone scan in low-risk patients, with different authors supporting various cut-off levels of PSA, with some including Gleason score and clinical stage. The European Association of Urology (EAU) guidelines, updated in March 2009, recommend that staging bone scan may not be indicated in patients with a PSA level of <20 with moderately to well-differentiated tumours in the absence of bony symptoms 15], while the American Urological Association and American Joint Committee on Cancer (AJCC) both recommend that staging bone scan is indicated in patients with a Gleason score of >7 or a PSA level of >20 prior to treatment 14].Despite this, there remains a large demand for isotope bone scanning in patients with a new diagnosis of prostate cancer regardless of risk stratification based on these prognostic tools.The purpose of the current study was to correlate PSA levels and Gleason scores with bone scan results in patients with newly diagnosed prostate cancer, with the aim of identifying a subgroup of patients who did not require staging bone scan, and assess the feasibility and safety of implementing EAU guidelines.