Patients presenting with symptoms of prostate cancer would have reached a stage at which curative interventions are usually not possible since the symptoms are often only present in the advanced stages. Detection of prostate cancer prior to the onset of symptoms is therefore necessary for adopting a curative line of management. With aggressive screening measures and good public awareness these days, almost 70% to 80% of the prostate cancers are currently diagnosed in the early stages. The early diagnosis is partly responsible for the recent fall in the prostate cancer related mortality in the US.
One of the most important clinical examination for evaluation of a patient for prostate cancer is the DRE (digital rectal examination). Simple screening tests like PSA (prostate specific antigen) estimation are usually performed to detect any individual at high risk for developing prostate cancer. Additional diagnostic tests are considered in patients with enlarged prostate, elevated PSA value, urological symptoms, or family history of prostate cancer.
Digital Rectal Examination for Prostate Cancer
DRE is a useful clinical examination but has a low sensitivity and specificity for diagnosis of prostate cancer. All suspected or abnormal DREs should be biopsied. A palpable nodule on DRE is one of the most common clinical finding that prompts biopsy leading to the diagnosis of prostate cancer. Other features may include a stony hard prostate with a loss of the median sulcus on the prostate gland.
PSA Screening and Diagnostic Tests
PSA screening tests include PSA levels, percent-free PSA, and PSA velocity values.
PSA level of more than 4 ng/mL is considered to be significant and has about 30% predictive value for prostate cancer (chance of detection of prostate cancer) at biopsy and 70 to 80% of tumors can be detected by this approach. The positive predictive value for PSA levels above 10 ng/mL increases to more than 60% for prostate cancer. More than 60% of prostate cancer patients are diagnosed when asymptomatic only because of the elevated PSA levels.
PSA velocity, percent-free PSA and PSA density are other PSA based screening tests.
The rate of change of PSA value over a period of time is referred as PSA velocity. Calculation of PSA velocity requires a minimum of 3 values of PSA levels collected over a period not less than 18 months. A PSA velocity value above 0.75 ng/mL per year is considered to be significant.
Percent-free PSA is the free PSA expressed as the ratio with total PSA. Men with prostate cancer have significantly lower percent-free PSA compared with men without prostate cancer. Percent-free PSA of less than 25% is considered to be clinically significant. The PSA density can be found by dividing the PSA value by the volume obtained with help of a trans-rectal ultrasound (TRUS).
Prostate Cancer Biopsy
A TRUS guided transrectal needle biopsy is performed to confirm diagnosis of prostate cancer in men :
- with a significant PSA based finding
- with an abnormal DRE
- whom prostate cancer is suspected
In a prostate biopsy, sextant biopsy specimens (base, midgland, and apex on each side) are usually obtained and in high risk patients seminal vesicles are also sampled. Other radiological studies as diagnostic aids for prostate cancer evaluation are usually employed when PSA levels above 10 ng/mL.
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Radiology and Imaging Investigations for Prostate Cancer
Transrectal Ultrasound (TRUS)
TRUS is the most important radiological investigation for the initial assessment of prostate cancer. Urologists use TRUS for guiding the needles in guided-biopsy. TRUS is also of use in prostate volume assessment and calculation of the PSA density. It is however not useful in assessing the involvement of the prostate capsule or the early extensions beyond the capsule. Use of Color duplex and power Doppler may help in specifically identifying the hypervascular areas that corresponds to the malignant lesions.
Computerized Tomography (CT Scan)
Prostate cancer evaluation often includes CT scan of the pelvis but its role is mostly limited to detection of lymph node metastases. The usefulness of CT scan in the detection of tumors confined to prostate tissue and quantification of extracapsular prostatic tumor is limited.
Magnetic Resonance Imaging (MRI)
MRI provides scope for assessment for extracapsular extension with better visualization of the prostatic capsule and provides a more detailed anatomic picture. The inclusion of MR spectroscopy improves the ability of MRI to localize prostatic cancer more accurately.
Radionuclide bone scan is considered to be the standard investigation to evaluate high-risk patients for the presence of bone metastases. It is not recommended for low-risk patients. Patients with PSA levels of less than 10 ng/mL have only minimal chance for a positive bone scan, while patients having PSA levels above 50 ng/mL have a 50% chance of positive bone scan. Response to treatment in advanced prostate cancer can also be assessed with bone scans.
Positron Emission Tomography (PET)
The introduction of new tracers (like C11 choline) in PET imaging has been found to significantly enhance its use to detect intraprostatic disease and metastases to lymph nodes.
Prostascint scanning utilizes monoclonal antibodies conjugated with radioisotopes to assess relapse of prostate cancer in patients with elevated PSA levels after primary therapy.