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Staging of prostate cancer
Prostate cancer is staged based on the TNM staging system or the number system. Staging with either system is based on the extent of the tumour in the prostate, the spread of the cancer locally in and around the prostate and into the lymph nodes, and the spread of cancer into other parts of the body. Based on these systems a stage is given after a diagnosis is made.
Prostate cancer can also be grouped into low, intermediate and high risk cancers, depending on the T stage, N stage, Gleason score and PSA levels. Here is an example of the different groups. Treatment decisions are based on these risk categories.
Once a prostate cancer is diagnosed, the following investigations can be done:
An MRI scan of the prostate is used to stage the prostate cancer locally that is to see the extent of spread of the cancer in and around the prostate. The scan also helps to assess the lymph nodes in the pelvis to see if they are enlarged. Enlarged nodes may suggest the spread of cancer into them. The MRI scan can be done before the biopsy or after the biopsy. An MRI can also be used to help to target the biopsy in patients who have had previous negative biopsies.
MRI scan picture
Isotope Bone Scan
An isotope bone scan is done to look for the presence of cancer in the bones. A radio isotope called Technitium99 is injected into the vein prior to the scan. The scan is reported as positive if cancer is detected in the bones. Prostate cancer is one of the cancers that spread to the bones. But the risk of its spread to the bones is dependent on the nature of the cancer. A bone scan is advised in intermediate and high risk cancers but is not needed in low risk cancers. Another type of bone scan called the F18 bone scan is also done in some centres. Either of these scans is good for staging purposes.
Bone scan picture
A CT scan is done in instances when an MRI is not available or when it is needed to assess the other parts of the body as part of the staging, particularly in high risk prostate cancer. A CT scan uses X-rays to get detailed images of the body.
A PET CT scan is not routinely recommended for the staging of prostate cancer as uptake of the radioactive tracer used in standard PET CT (18 FDG) is not consistently taken up by the cancer cells. Newer PET CT tracers such as 18 F-Choline PET are said to be more useful in this setting.