Determining the extent of prostate cancer is important for predicting the course of the disease and in choosing the best treatment. Results from the digital rectal exam (DRE), prostate-specific antigen (PSA) tests, and prostate biopsy, give the urologist a good idea of whether the cancer is confined to the prostate or has spread outside the gland. The pathologist’s examination of the biopsy specimen is crucial.
After studying the characteristics of the tumor, the pathologist assigns a Gleason score to the cancer. The Gleason score provides an estimate of how aggressive the cancer is. Depending on the Gleason score and the initial PSA results, the physician may order imaging studies to determine whether the cancer has spread to distant sites.
What is a Gleason score?
The most important factor in predicting the current state of the prostate cancer and the success of any treatment is the Gleason score. This score is based on tumor grade, which is an indication of the tumor’s aggressiveness. The tumor grade reflects how far the cancer cells deviate from normal, healthy cells.
Normal prostate epithelial cells form highly organized glands, with well-defined borders. Cancer cells, in contrast, display various degrees of disorganization and distortion.
Cancers whose cells appear closest to normal are considered grade 3 and generally are the least aggressive; those with highly irregular, disorganized features are classified as grade 4 or 5 and generally are the most aggressive.
The Gleason score is derived by determining the two most prevalent organizational patterns in the tumor, assigning each a grade and then adding the two numbers together. For example, if the most common pattern—the primary grade—is 3 and the next most common pattern—the secondary grade—is 4, the Gleason score would be 7 or 3+4. But if the primary grade is 4 and the secondary grade is 3, the Gleason score would be 4+3, and this would be considered to be more aggressive.
In other words, the primary grade carries more weight than the secondary pattern in determining the aggressiveness of the cancer. In some cases the pathologist will report a tertiary pattern that is associated with prognosis but is not a part of the overall score. For example, a pathologist may report that the biopsy shows a Gleason 3+3 (score 6), with a tertiary pattern 4.
Most doctors classify a Gleason score of 6 as a low-grade tumor, a Gleason score of 7 as intermediate, and Gleason scores of 8, 9 and 10 as high grade. Gleason scores of 8 to 10 are associated with the least favorable outlook.
Some men will need to undergo a bone scan to determine whether their prostate cancer has spread to the bones. The bone scan involves intravenous injection of a radioactive substance that is preferentially taken up by the damaged bone. (Bone can be damaged by cancer as well as by osteoporosis and other bone diseases.) A special scanner is then used to detect the radioactivity. Areas of the body that show increased radioactivity have bone damage, possibly because cancer has spread to the bone.
A bone scan is not typically ordered when PSA levels are less than 10 ng/mL because the likelihood of cancer spread is very low. Men who have a PSA level of 20 ng/mL or higher, a Gleason score of 8 to 10, or disease extensive enough to be felt on both sides of the prostate or beyond the prostate should have a bone scan and a computed tomography (CT) scan of the pelvis.
A ProstaScint scan may be used to look for prostate cancer cells that have spread to the lymph nodes or soft organs. It uses antibodies that attach to a protein called prostate-specific membrane antigen on prostate cancer cells. These antibodies mark cancer cells with a radioactive isotope that is then picked up by a special scanner. This scan is not considered very accurate, but it may be used when PSA levels start to rise again after surgery or radiation therapy.
If the DRE, PSA, and Gleason score suggest that the cancer has spread, CT or magnetic resonance imaging (MRI) may be performed to look for enlarged lymph nodes. The urologist may recommend a laparoscopic biopsy. In this procedure, a surgeon uses a laparoscope (an instrument with a tiny light and camera) to view the lymph nodes near the prostate and take samples to check for cancer.
New approaches for detecting the presence or progression of prostate cancer are being investigated. These include positron emission tomography (PET) and PET/CT. Further development of these imaging procedures may provide more precise ways to diagnose recurrences and locate metastases (cancers that have spread).
After gathering this information, the physician can then describe the clinical stage (or extent) of the cancer. Clinical stage takes into account whether the cancer has spread to the lymph nodes, bones, or other areas. One of two methods is used—the Whitmore-Jewett method or, more commonly, the TNM (tumor, node, metastasis) system.
The National Comprehensive Cancer Network (NCCN), an association of 23 cancer treatment centers, convenes expert panels to make recommendations for diagnosis and treatment of cancers, including prostate cancer. Currently, the NCCN recommends that after a diagnosis of prostate cancer is made, the man should be categorized in one of four categories to help determine optimal management.
The categories are: very low risk, low risk, intermediate
risk and high risk. The determination is based on PSA level, prostate size, needle biopsy findings and the stage of cancer.