Predictive value of serum prostate specific antigen in detecting bone metastasis in prostate cancer patients using bone scintigraphy

INTRODUCTION: Radionuclide bone scan (BS) used to be the investigation of choice for detecting osseous metastases in prostate cancer. Now, with the availability serum prostate specific antigen (PSA) testing, clinicians do have a timely, cost-effective method to determine those patients who are highly unlikely to have osseous metastases. We determine the utility of PSA for predicting the presence of skeletal metastasis on BSs in prostate cancer patients. MATERIALS AND METHODS: Retrospective analysis of medical records of 322 consecutive prostate cancers patients subjected to BS during the last 3 years was done. 52 cases were excluded due to following reasons: Serum PSA not available, hormonal or other therapy given prior to serum PSA measurement, and/or BS, and symptomatic for bone metastasis. In remaining 270 cases, PSA value and BS were evaluated. BS was performed with Tc99m methylene diphosphonate (MDP) as per the standard protocol. RESULTS: BS was found to be positive in 153/270 (56%) and negative in 117 (46%) patients. Of the 153 positive cases, 108 (70%) had serum PSA > 100 ng/ml, 42 (28%) had PSA of 20-100 ng/ml and only 3 (2%) had PSA < 20 ng/ml. All the patients with PSA > 100 ng/ml had multiple skeletal metastasis. Of the 117 negative cases, 110 (94%) had a PSA < 20 ng/ml, 5 had between 20 and 100 ng/ml and only 2 (1.8%) had PSA > 100 ng/ml. Of the 113 patients with serum PSA < 20 ng/ml, 110 (97.4%) did not show any bony metastasis. 150/157 (95.5%) patients with PSA > 20 ng/ml had bone metastasis. Using this criterion, 110 (40.7%) scans would have been omitted. CONCLUSIONS: Serum PSA < 20 ng/ml have high predictive value in ruling out skeletal metastasis. Our data are in corroboration with results from previous studies that BS should be performed only if PSA > 20 ng/ml. Using this cut-off, unnecessary investigation can be avoided. Avoiding BS in this group of patients would translate into a significant cost-saving and reduction in their psychological and physical burden.