Prostate cancer happens when cells in the prostate begin to grow out of control and can then invade nearby tissues or spread throughout the body. Large collections of this out of control tissue are called tumors. However, some tumors are not really cancer because they cannot spread or threaten someone's life. These are called benign tumors. The tumors that can spread throughout the body or invade nearby tissues are considered cancer and are called malignant tumors. Usually, prostate cancer is very slow growing. However, sometimes it will grow quickly and spread to nearby lymph nodes. Lymph nodes are small, pea-sized pieces of tissue that filter and clean lymph, a clear liquid waste product. If prostate cancer has spread to your lymph nodes when it is diagnosed, it means that there is higher chance that it has spread to other areas of the body.
How is prostate cancer diagnosed and staged?
If you have symptoms suspicious for prostate cancer, your doctor will do a digital rectal exam and a PSA blood test. If either of those two test is abnormal, then most likely your doctor will recommend that you receive a biopsy. Also, your doctor may want to get a biopsy if there is an abnormal result on a screening PSA or digital rectal exam. A biopsy is the only way to know for sure if you have cancer, because it allows your doctors to get cells that can be examined under a microscope. The most common way that a biopsy is done is with a transrectal ultrasound (TRUS). A transrectal ultrasound is a thin cylinder that emits sound waves and monitors them when they bounce off of tissue. It is inserted into your rectum, and allows your doctor to view your prostate and choose where to remove tissue from. Any suspicious areas are biopsied, plus some tissue will be removed from all of the different parts of the prostate (to make sure they don't miss any cancers that may be small and growing in one particular area). The procedure is done while you are awake, with the help of some numbing medicine. Unfortunately, a transrectal ultrasound isn't a perfect tool because even though many samples are taken, it can occasionally miss the area of the cancer. If this happens, and your PSA remains elevated, you will probably need to have the procedure repeated in a few months.
Once the tissue is removed, a doctor known as a pathologist will review the specimen. The pathologist can tell if it is cancer or not; and if it is cancerous, then the pathologist will characterize it by what type of prostate cancer it is and how abnormal it looks (known as the grade). The vast majority of all prostate cancers (at least 95%) are a subtype known as adenocarcinoma, but occasionally they can be small cell carcinomas or lymphomas (two rare types of prostate cancer that are treated differently than the more standard adenocarcinomas). The pathologist then characterizes how much the cancer looks like normal prostate tissue, and this is known as the grade of the tumor. Pathologists often use a scale when they grade prostate tumors known as the Gleason score. The Gleason score runs from 2 to 10, with 2 being a very normal looking tumor and 10 being a very abnormal looking tumor. Generally, the more abnormal the tumor looks, the more aggressive it is. We characterize grades on a scale because, together with staging, it gives us a way to offer a prognosis and it often guides our choice of therapy.
Prostate cancer is divided into four different stages to help guide our treatments and offer information about the chances for a cure. This staging is done in a limited fashion before surgery taking into account whether or not the tumor can be felt on digital rectal exam and the results of any imaging modalities; it is done definitively after a surgical procedure that removes lymph nodes and allows a pathologist to examine them for signs of cancer. The staging system is somewhat complex, but here is a simplified version of it:
Tumor cannot be felt during a digital rectal exam; it was detected by an elevated PSA blood test or incidentally found during another prostate procedure for a benign condition.
Tumor can be felt during a digital rectal exam, but it has not spread beyond the prostate and it hasn't spread to lymph nodes or other organs.
Tumor extends outside the prostate and can be in the seminal vesicles, but not in any other organs or lymph nodes.
Tumor has spread to other organs or lymph nodes.
Although the clinical stage is important, the pathological stage is a more accurate predictor of the course of your cancer because it actually examines the prostate and the lymph nodes in the area. If your stage, grade, or PSA are high enough, you may be referred for other tests before treatment to look for spread to other parts of your body. Tests like CT scans (a 3-D x-ray) or MRIs (like a CT scan but done with magnets) can examine the prostate and localized lymph nodes. Some patients are referred for a bone scan, which is a test using a radioactive tracer to look for metastasis to any of your bones. Another test that you may be referred for is called a ProstaScint scan, which uses a radioactive tracer that can localize prostate cancer to either bones or lymph nodes. Finally, if your doctors are very worried about spread to lymph nodes, they may choose to perform a surgical lymph node sampling before proceeding with any definitive treatment.