Influence of local tumour stage and grade on reliability of serum prostate-specific antigen in predicting skeletal metastases in patients with adenocarcinoma of the prostate

Objective: To determine whether serum prostate-specific antigen (PSA) can b e reliably used to predict the absence or presence of skeletal metastases o n the bone scan in patients with adenocarcinoma of the prostate. Methods: W e studied 450 consecutive men presenting with adenocarcinoma of the prostat e between 1991 and 1995. Serum PSA was measured by the Hybritech Tandem-R m onoclonal immunoradiometric assay and bone scanning was performed with 99m- technetium-labelled methylene diphosphonate. In total, 46 patients were exc luded for one or more of the following reasons: serum PSA not available; ra dionuclide bone scan inconclusive; histology of the prostate other than ade nocarcinoma; hormonal or other therapy given prior to obtaining the serum P SA and/or bone scan. Results: Of the 404 patients induced, 43% had poorly d ifferentiated (grade 3), 74% had locally advanced (stages T3-4) tumours and 50% had skeletal metastases. The mean and median serum PSA were 348 and 52 ng/ml, respectively, and 77% of the patients had a serum PSA >20 ng/ml. Th e negative predictive value (for the absence of metastases on bone scan) of a serum PSA <20 ng/ml was 87% for the whole group of patients, 92, 94 and 70% for grade 1, 2 and 3 tumours, and 95, 83 and 50% for stage T1-2, T3 and T4 tumours, respectively. The positive predictive value (for the presence of metastases on bone scan) of a serum PSA >100 ng/ml was 80% for the whole group of patients. Conclusions: In patients presenting with adenocarcinoma of the prostate, serum PSA alone is not sufficiently reliable to predict t he absence or presence of metastases on the radionuclide bone scan. In pati ents with grade 3 and clinical stage T3-4 tumours, a bone scan should be ob tained for accurate staging, regardless of the serum PSA value.