Tumor Grade and Prostate Cancer Staging
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, 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.
The Gleason Score
The most important factor in predicting the current state of the prostate cancer and its probable outcome 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 cells are highly organized, with well-defined structures. Cancer cells, in contrast, display various degrees of disorganization and distortion. Cancers whose cells appear closest to normal are considered grade 1 and generally are the least aggressive; those with highly irregular, disorganized features are classified as grade 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 is grade 3 and the next most common pattern is grade 4, the Gleason score would be 7. Most pathologists do not recommend assigning Gleason scores below 5 based on needle biopsies because when the prostate is removed and the entire gland is evaluated, lower Gleason scores are almost always upgraded.
Most urologists classify Gleason scores of 5 and 6 as low-grade tumors, a Gleason score of 7 as intermediate, and Gleason scores of 8, 9, and 10 as high grade, with the least favorable outlook.
With the latest pathology techniques, it is sometimes possible to detect three different grades within the same biopsy. This can make deriving a Gleason score more complicated. A panel of international experts has recommended modifications in the grading system that account for these situations. These modifications are expected to be broadly adopted in the coming years.
Imaging Studies to Stage Prostate Cancer
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.
Some physicians do not order a bone scan when PSA levels are less than 10 ng/mL because the likelihood of cancer spread is very low. Others prefer to order a scan, even if the risk of spread is low, to obtain a baseline measurement for comparison if a bone scan is needed at a later date.
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.
The ProstaScint scan may be used to look for prostate cancer cells that have spread to the lymph nodes or soft organs. ProstaScint 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. The ProstaScint scan is not considered very accurate. It is usually used when PSA levels start to rise again after surgery or radiation therapy.
If the digital rectal exam, PSA, and Gleason score suggest that the cancer has spread, computed tomography (CT) or magnetic resonance imaging (MRI) may be performed to look for enlarged lymph nodes. In some instances, 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 usedthe Whitmore-Jewett method or, more commonly, the TNM (tumor, node, metastasis) system.