Prostate Cancer: Detection, Diagnosis and Staging
How is prostate cancer diagnosed?
Prostate cancer rarely causes any symptoms until it has progressed to an incurable stage. As a result, the best way to diagnose prostate cancer is through screening during an annual physical examination. Screening involves a digital rectal exam (finger exam) and a prostate specific antigen (PSA) blood test.
The National Comprehensive Cancer Network currently recommends men age 45 and older should consider being screened for prostate cancer. Patients with relatives who have prostate cancer and African-American patients are at higher risk. If either the digital rectal exam or PSA is abnormal, a prostate biopsy is performed to determine if cancer is present.
What is the digital rectal exam?
The digital rectal examination can detect cancer and determine whether it is confined to the prostate. Because the prostate lies in front of the rectum, a physician can feel the prostate by inserting a gloved, lubricated finger into the rectum. Many times, early cancers are not able to be felt by rectal examination because they are too small.
What is PSA?
Prostate specific antigen (PSA) is a protein produced by both normal and cancerous prostate cancer cells. When prostate cancer grows or when other prostate diseases are present, the amount of PSA detected in the blood often increases. Currently, an increased PSA level is the most common way to detect prostate cancer.
How is a prostate biopsy performed?
First, a transrectal ultrasound of the prostate is performed to examine the prostate. Ultrasonography allows the urologist to measure the size of the prostate and see if there are any suspicious areas. The urologist also uses the ultrasound to direct a local anesthetic into the prostate area to numb it before the prostate biopsy. A spring-loaded needle is then placed through the ultrasound probe, and then, using the ultrasound to target certain areas of the prostate, 10 to 14 biopsies are typically performed. Each biopsy removes a small core of tissue, which are then examined under a microscope to see if prostate cancer cells are present.
How is prostate cancer graded?
A pathologist named Donald Gleason described the grading system for prostate cancer based on the pattern of cancer cells, and this is now called the Gleason score. The Gleason score reflects how aggressive the prostate cancer is likely to behave. Each area of prostate cancer is graded on a numeric scale of 1 to 5 (with 5 being the most aggressive). The pathologist looks at all of the biopsies and then assigns a grade to the two most common patterns seen. These two grades are then added together to determine the Gleason score or Gleason sum. Therefore, the resulting Gleason score will always be a number between 2 to 10 (e.g., 3 + 4 = 7/10). These days, it is rare to see cancers with a score of 2 to 5. Most cancers are either a 6 or higher. The higher the number, the more aggressive the prostate cancer is anticipated to behave.
How do you stage prostate cancer?
Stage refers to whether cancer is confined to the prostate or appears to have spread to other areas of the body. For most men with early cancers, there’s such a low chance of having cancer elsewhere in the body that further testing is not typically warranted. However, there are several tests that may be useful in determining tumor stage, including:
- CT Scan: Computed tomography (CT scan) is an x-ray procedure that provides detailed images of the body. It can help to detect lymph nodes in the pelvis that are enlarged because of cancer. This test is usually used for intermediate or high-risk patients only.
- MRI: Magnetic resonance imaging (MRI) is similar to a CT scan except that it uses magnetic fields instead of x-rays to create internal pictures of the body. While standard MRI has limited additional usefulness for prostate imaging, a new MRI technology called multiparametric MRI is sometimes useful for determining whether cancer is extending outside the prostate near the nerves that control erections.
- Bone scan: This test is performed when there is suspicion that cancer has spread to the bone. A small amount of radioactive tracer material is injected into the bloodstream; a few hours later, a scanner is used to pinpoint areas where the tracer material collects. When this tracer material collects in the bone, it is concerning because cancer may have spread into the bone.
- Lymph node dissection: The lymph nodes are usually the first location where prostate cancer spreads once it leaves the prostate. Using information such as PSA level, digital rectal exam results and Gleason score, the urologist can estimate the risk that cancer has spread to the lymph nodes. If there is a very low risk that the cancer has spread, a lymph node dissection is not typically performed. If there is a higher chance of lymph node spread, they are sometimes sampled in the operating room to more accurately stage a patient’s cancer.
What is clinical stage?
Clinical tumor stage refers to whether or not the tumor can be palpated or felt on exam and whether it may have spread outside the prostate. The tumor-node-metastasis system (TNM) is used to designate the clinical stage.
The information below is from the American Joint Committee on Cancer, 7th edition, 2010
Evaluation of the (primary) tumor ('T')
- TX: cannot evaluate the primary tumor
- T0: no evidence of tumor
- T1: tumor present, but not detectable clinically or with imaging
- T1a: tumor incidentally found in < 5% of prostate tissue resected (for other reasons)
- T1b: tumor incidentally found in > 5% of prostate tissue resected (for other reasons)
- T1c: tumor found in a needle biopsy performed due to an elevated serum PSA
- T2: tumor can be felt (palpated) on examination, but has not spread outside the prostate
- T2a: tumor palpated in half or less than half of one of the prostate gland’s two lobes
- T2b: tumor palpated in more than half of one lobe of the prostate
- T2c: tumor palpated in both lobes of the prostate
- T3a: tumor spread through the capsule on one or both sides of the prostate
- T3b: tumor has invaded one or both seminal vesicles
- T3: tumor palpated on examination and appears to have spread through the prostatic capsule
- T4: tumor has invaded other nearby structures/organs
Evaluation of the regional lymph nodes ('N')
- NX: cannot evaluate the regional lymph nodes
- N0: there has been no spread to the regional lymph nodes
- N1: there has been spread to the regional lymph nodes
Evaluation of distant metastasis ('M')
- MX: cannot evaluate distant metastasis
- M0: there is no distant metastasis
- M1: there is distant metastasis
- M1a: the cancer has spread to lymph nodes beyond the regional ones
- M1b: the cancer has spread to bone
- M1c: the cancer has spread to other sites (regardless of bony involvement)
What is low risk, intermediate risk or high risk prostate cancer?
Prostate cancers can be classified based on clinical stage, PSA level and Gleason score into risk categories. This is important for deciding what treatments may be most appropriate. Also, it is useful for determining long term prognosis.
- Low Risk: clinical stage T1c or T2a, serum PSA of <10 ng/ml, AND biopsy Gleason score of 6 or less
- Intermediate Risk: clinical stage T2b, serum PSA 10-20 ng/ml OR biopsy Gleason score of 7
- High Risk: clinical stage T2c or higher, serum PSA >20 ng/ml OR biopsy Gleason score of 8 or higher