This section will describe how prostate cancer is formally diagnosed, how it is graded to estimate its aggressiveness, how it is staged to describe its extent, and the procedures commonly used to accomplish these tasks.
A number of tests may be used to formally diagnosis prostate cancer.
Core Needle Biopsy
Samples of prostate tissue must be examined by a pathologist in a laboratory to make a formal diagnosis of prostate cancer. These samples usually are obtained by a core needle biopsy procedure, in which a fine needle is inserted into the prostate to withdraw small samples of tissue. The biopsy is done as an outpatient procedure and local anesthesia is usually preferred.
Transrectal ultrasound (TRUS) guided biopsy
This test uses sound waves produced by a small probe placed in the rectum to create an image of the prostate on a video screen. The echoes from the waves are translated by a computer into a picture, which can show the location of more suspicious or abnormal areas of the prostate.
Since cancer, even if present, may not be seen with the TRUS, it is important to sample the entire prostate gland. An instrument called a biopsy gun quickly inserts and removes narrow needles, obtaining small cores of tissue that are sent to the laboratory for examination. From six to 18 cores may be removed from different areas of the prostate, especially from the more suspicious locations.
The procedure takes less than half an hour, and usually causes only a little discomfort and occasionally some bleeding. An antibiotic such as Ciproflaxacin is usually given before and after the procedure to reduce risk of infection.
Sometimes, the first biopsy doesn't reveal the presence of cancer even when cancer is strongly suggested by the patient's symptoms or PSA test results. Repeat biopsies may be required before the cancer is actually discovered.
The percentage of biopsy cores containing cancer tissue and the percentage of cancerous tissue in individual cores are useful measures of the extent of the cancer. The transrectal ultrasound also can provide valuable information about whether the cancer has reached the edge of or broken through the capsule of the prostate gland. It also provides an estimate of the size of the prostate.
Lymph Node Biopsy
Once a cancer diagnosis has been confirmed and if the transrectal ultrasound or other findings suggest there may be possible spread of the cancer, a lymph node biopsy may be done to determine whether the cancer has spread to the nearby lymph nodes. If the degree of cancer spread and lymph node involvement is more extensive, a radical prostatectomy may not be attempted and other treatment options will be considered.
The lymph nodes can be removed for evaluation by three different methods:
- One is through an incision in the lower abdomen, often at the time that a planned radical prostatectomy is to begin. The nodes are examined in the laboratory while the patient is under anesthesia. The findings may help determine whether or not the surgery should proceed.
- Samples of lymph node cells also can be obtained by a procedure called fine needle aspiration. A CT scan image is used to guide a long, thin needle into the lymph nodes to obtain these samples.
- Another option is laparoscopic lymph node dissection.
Radionucleide Bone Scan
A radionucleide bone scan can show whether the cancer has spread from the prostate to the bones. Some low-level radioactive material is injected and will be taken up by diseased bone cells. This allows the location of diseased bone to be seen on the total body bone scan image. These areas may suggest that metastatic cancer is present, although arthritis and other bone diseases could create the same pattern.
Usually, a bone scan is not ordered unless there are signs of aggressive disease such as a markedly elevated PSA level, a high Gleason score (a prostate cancer grading system described below) or a large tumor.
Computed tomography (CT) Scan
CT scan uses a rotating X-ray beam to create a series of pictures of the body from many angles that can be put together into a detailed cross-sectional image. This can help reveal abnormally enlarged pelvic lymph nodes, or spread of the cancer to other internal organs. A CT scan usually isn't ordered unless there is a markedly elevated PSA, a high Gleason score, or evidence of a large tumor.
Magnetic Resonance Imaging (MRI)
MRI is like a CT scan, except magnetic fields are used instead of X-rays to create the detailed images of selected areas of the body. These scans are less effective in revealing microscopic-sized cancers, although an MRI using a rectal coil is superior to a routine pelvic MRI.
A modification of the MRI that is still considered experimental, called magnetic resonance spectroscopy imaging (MRSI), may provide more precise information on where the cancer is located in the prostate gland and the surrounding area.
Grading the Cancer
If cancer is found in the prostate biopsy sample, it is graded to estimate its aggressiveness. The most commonly used prostate cancer grading system is called the Gleason system.
The pathologist examines the cancer cells under a microscope and evaluates how closely the arrangement of the cancer cells matches that of normal prostate cells. For each sample, two gradings are made of the most common and next most common cancer cell patterns, on a scale of 1 (most like normal cells) through 5 (least like normal cells). The two grades are then added (e.g., 3+2=5) to give the Gleason score, with a range of 2 to10.
The Gleason score is essential for treatment planning and decision making. Every prostate cancer patient should know his Gleason score. Those with low scores (4 or less) are more likely to have a less aggressive, slower growing cancer. Gleason 5 and 6 are the most common scores, and indicate that the cancer is more intermediate in nature. Gleason 7 is transitional, and Gleasons of 8 to10 are high and indicate cancers that could grow and spread more rapidly.
Since the most accurate grading of the cancer is, in part, a function of the skill and experience of the pathologist, it may be appropriate in some cases to get a second opinion for the Gleason score.
Staging the Cancer
A prostate cancer's stage indicates how far it has spread, and is very important in selecting treatments and in predicting prognosis or the future of the disease. The commonly used staging system in the United States is the TNM system. This describes:
- The extent of the primary tumor (T)
- The absence or presence of metastasis to nearby lymph nodes (N)
- The absence or presence of distant metastasis (M)
There are two types of T classifications for prostate cancer. The clinical stage is based on the digital rectal examination, needle biopsy and transrectal ultrasound findings. The pathological stage is based upon surgical removal of the entire prostate gland, the seminal vesicles (two small sacs that store semen), and sometimes nearby lymph nodes.
The clinical stage is used in making treatment decisions, but may underestimate the extent of cancer development and spread. The pathological stage is more accurate in making a prognosis and indicating the need for further treatment. However, it can be determined only with patients who have had a radical prostatectomy.
- T1Refers to a tumor that is not felt during a digital rectal exam. T1a (5 percent or less of specimen involved in tumor) and T1b (more than 5 percent tumor involved) describe cancers found incidentally during a TURP, or transurethral resection of the prostate, a surgical procedure done to relieve symptoms of benign prostatic hyperplasia, where examination of the removed prostate tissue reveals cancer. T1c cancers are those detected by PSA only and which are then diagnosed with a biopsy.
- T2Refers to a cancer that is felt by the doctor during the digital rectal examination, or is seen with a transrectal ultrasound, and is believed to be confined within the prostate gland. If one lobe of the prostate is involved, the stage is T2a. If both lobes have tumors, the stage is T2b.
- T3Refers to a cancer that has extended beyond the capsule of the prostate and/or to the seminal vesicles. If the cancer is outside the prostate on one or both sides, the stage is T3a. If the seminal vesicles are involved, it is T3b.
- T4The cancer has spread to other tissues next to the prostate, such as the bladder's external sphincter that helps control urination, the rectum and/or the wall of the pelvis.
- N0Means the cancer has not spread to any lymph nodes
- N1Indicates spread to one or more pelvic lymph nodes
- NxIndicates that regional lymph nodes cannot be assessed
- M0Means the cancer has not metastasized beyond the regional nodes.
- M1Means metastases are present in distant lymph nodes, in bones, and/or other distant organs such as lungs, liver or brain. The site(s) of the metastases may be specified.
- MxIndicates that distant metastases cannot be assessed.
- Next: Treating Prostate Cancer
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UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.
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