Predicting bone scan positivity: The utility of PSA doubling time versus absolute PSA levels

1. No. 154 Predicting bone scan positivity:The utility of PSA doubling time versus absolute PSA levels Patrick Preece, Henry Yao, Sky Chew, Danny Liew, Richard McMullin Ballarat Urology, Royal Melbourne Hospital Posters Proudly Supported by: Introduction Asymptomatic men with prostate cancer and increasing PSA levels are often investigated with periodic bone scans. However, the yield of positive studies is low. PSA doubling time (PSADT) is an alternative marker of cancer progression . However the comparative utility of PSADT and PSA in predicting bony metastases is largely unknown. Results Aims To determine if PSADT is a better predictor of bone scan positivity for metastatic prostate cancer compared to absolute PSA levels. To develop a rule to guide appropriate ordering of bone scans to assess for the development of distant metastases in men with prostate cancer. To reduce the number of unnecessary bone scans. ROC curve analysis: -PSADT outperformed tPSA as a predictor of bone scan results, where Area Under the Curve (AUC)= 0.75 vs. 0.84 (p=0.02) -For the composite measure R= tPSA/PSADT, AUC= 0.86. No significant difference compared to PSADT (p=0.39) -For a given sensitivity of 98.55%, PSADT has a specificity of 38.32% and tPSA of 17.13%. A sensitivity of 98.55% corresponds to a PSADT of 18 months. ADT subgroup: -Lower tPSA and PSADT in those all exposed to ADT -AUC (tPSAvs PSADT)= 0.62 vs 0.77 (p=0.33) -For a given sensitivity of 98.55%, PSADT has a specificity of 27.27%. MethodsPSA measurements were retrospectively analysed for 390 men with prostate cancer who had a 99mTc radionuclide bone scan between 2009 and 2012 and met no exclusion criteria, including: -Previous bone scan suggestive of metastatic disease, -A history of non-prostate malignancy, and -Any prostate specific condition, procedure or treatment that occurred between the two PSA levels used to calculate doubling time. Trigger PSA (tPSA) was defined as the most recent PSA level not preceding a bone scan by more than three months. PSADT (months)= log2 x dT/(log(PSA1)-log(PSA2)) All bone scans (BS) were performed at a single facility. PSA levels were analysed at the same laboratory for any given patient. ConclusionsPSADT performs better than tPSA as a predictor of new bone metastases. In the absence of clinical reasons to suspect metastatic disease, it may be appropriate to withhold ordering a bone scan in the setting of rising PSA levels until the PSADT is less than 18 months; this has a sensitivity of 98.55% and a specificity of 38.32%. A lower threshold may be needed for patients on ADT. If PSADT ≤18 months was the threshold for ordering a BS in this cohort: -125 /390 scans would not have be performed (32.05% fewer scans) -67/ 69 patients with metastases would have been investigated (2.90% missed) References1. Z. Dotan, F. Bianco et al. Pattern of Prostate-Specific Antigen (PSA) Failure Dictates the Probability of a Positive Bone Scan in Patients With an Increasing PSA After Radical Prostatectomy, Journal of Clinical Oncology 23:9 p1962, 20052. M. Ng, N. Van As et al. Prostate-specific antigen (PSA) kinetics in untreated, localized prostate cancer: PSAV vs PSA doubling time, BJU International 103, 872-876, 2008 Acknowledgements StataCorp. 2011. Stata Statistical Software: Release 12. College Station, TX: StataCorp LP.