Following a positive diagnosis of prostate cancer, staging investigations are conducted to determine the pattern of disease spread according to the TNM classification (see section on pattern of disease spread under classification). The principal investigations are DRE, PSA testing and bone scanning, supplemented with computed tomography (CT) or magnetic resonance imaging (MRI) and chest X-ray in specific situations.1. The outcome of staging investigations will have a major impact on treatment decisions.
T-staging
T-staging refers to assessment of the primary tumour. The distinction between intracapsular (T1/T2) and extracapsular disease (T3/T4) is particularly important regarding treatment.1 Although digital rectal examination (DRE) may underestimate the degree of tumour extension, further investigations for T-staging are recommended if they will directly affect the treatment decision (i.e. if radical therapy becomes an option following the T2/T3 distinction).1 If this is the case, MRI is currently the most accurate modality for T-staging in men with prostate cancer.2
N-staging
Evaluation of lymph node involvement is necessary if it will affect the treatment decision, which is usually the case if potentially curative therapy is being considered.1 Patients with PSA <20ng/ml, T-stage T2a or less and Gleason score ≤6 have a low risk (<10%) of nodal metastasis may not undergo N-staging before potentially curative therapy.1 Imaging for determination of N-stage has limitations and surgical lymphadenectomy remains the gold standard for establishing nodal status.1
M-staging
Bone scanning (scintigraphy) is the usual imaging modality for detecting skeletal metastasis.1 Although sensitive, it is not diagnostically very specific, so patients often require additional imaging to confirm suspicious bone scan readings3. Since PSA level is a major predictor of positive bone scan4, this investigation may not be indicated in asymptomatic patients with PSA <20ng/ml and low or intermediate Gleason score.1 Other sites of metastatic spread include distant lymph nodes, lungs, liver, brain and skin, but further investigations are indicated if symptoms suggest the presence of soft-tissue metastases.1
References:
1. European Association of Urology. Guidelines on prostate cancer, 2010.
2. National Institute for Health and Clinical Excellence. Clinical guideline 58. Prostate cancer, February 2008.
3. Lecouvet FE, Geukens D, Stainier A, et al. Magnetic resonance imaging of the axial skeleton for detecting bone metastases in patients with high-risk prostate cancer: diagnostic and cost-effectiveness and comparison with current detection strategies. J Clin Oncol 2007;25:3281-7.
4. Lee N, Fawaaz R, Olsson CA, et al. Which patients with newly diagnosed prostate cancer need a radionuclide bone scan? An analysis based on 631 patients. Int J Radiat Oncol Biol Phys 2000;48:1443-6.