Most men are diagnosed with prostate cancer at an early clinical stage and do not have detectable metastases. Therefore, they generally do not have to undergo staging tests, such as a bone scan, computed tomography (CT), or magnetic resonance imaging (MRI). However, staging studies are done if there is clinical suspicion of metastasis, such as bone pain; local tumor spread beyond the prostate capsule; or a substantial risk of metastasis (prostate-specific antigen [PSA] >20 ng/ml and Gleason score >7).
Tests used to determine stage include the following:
- Radionuclide bone scans.
- Serum PSA level.
- Pelvic lymph node dissection (PLND).
- Transrectal or transperineal biopsy.
- Transrectal ultrasound (TRUS).
- CT scans.
Radionuclide bone scans
A radionuclide bone scan is the most widely used test for metastasis to the bone, which is the most common site of distant tumor spread.
Serum prostate-specific antigen (PSA) level
Serum PSA can predict the results of radionuclide bone scans in newly diagnosed patients.
- In one series, only 2 of 852 patients (0.23%) with a PSA of less than 20 ng/ml had a positive bone scan in the absence of bone pain.
- In another series of 265 prostate cancer patients, 0 of 23 patients with a PSA of less than 4 ng/ml had a positive bone scan, and 2 of 114 patients with a PSA of less than 10 ng/ml had a positive bone scan.
Magnetic resonance imaging (MRI)
Although MRI has been used to detect extracapsular extension of prostate cancer, a positive-predictive value of about 70% and considerable interobserver variation are problems that make its routine use in staging uncertain. Ultrasound and MRI, however, can reduce clinical understaging and thereby improve patient selection for local therapy. MRI with an endorectal coil appears to be more accurate for identification of organ-confined and extracapsular disease, especially when combined with spectroscopy. MRI is a poor tool for evaluating nodal disease.
MRI is more sensitive than radionuclide bone scans in the detection of bone metastases, but it is impractical for evaluating the entire skeletal system.