Staging is a process of measuring how far the cancer has spread in the body using several diagnostic tests. After the staging process, the doctors can determine which treatment to use to manage the cancer. The stages of prostate cancer can be either of the clinical or the pathological type.

In the clinical stages, the MRI scans, CT scans, X-rays, etc., are used to determine the extent of cancer. This information is represented by the Gleason score. Pathological staging is dependent on the information found during the lab tests conducted on prostate tissue removed during surgery.

Stages of prostate cancer based on Gleason grades
The Gleason grading system is based on how the cancerous cells look under the microscope when compared to healthy tissue and their arrangement in the prostate. The score is allotted as follows:

• Grade 1
  The cancerous cells in this grade look very similar to the regular cells of the prostate. The glands are closely-packed together, look small and well-formed.
• Grade 2
  While the glands are still well-formed, there is more tissue between them, and they look larger.
• Grade 3
  The tissue cells look normal and have well-formed glands. However, the cells begin to grow darker. On magnifying, it can be seen that some cells are leaving the glands and are spreading to nearby tissue. This stage can signify a less aggressive form of prostate cancer.
• Grade 4
  The prostate tissue contains very few cells that look normal. These cells have begun invading the surrounding tissue.

Grade 5
Very few glands can be seen on the prostate tissue. Most surrounding tissue contains sheets of cancerous cells.

Different stages of prostate cancer
The stages of prostate cancer are determined using three factors – the location and size of the tumor, whether or not cancer has spread to the lymph nodes and organs, and the extent of this spread. The four stages of prostate cancer are:

• Stage I
  In this stage, the cancer is slow-growing and cannot be detected through a rectal exam. The cancerous cells look similar to healthy cells and are restricted to the prostate. At this stage, the Gleason score would be 6 (grade 1), and the PSA levels would be 10 or less. Also, the tumor would be on only one-half of one side of the prostate.
• Stage II
  In stage II, the cancer might be restricted to the prostate, but the tumor can be felt during a rectal exam. While the PSA levels are still less than 20, the cancer cells start spreading more aggressively. The cancer cells may or may not be differentiated.
• Stage III
  At this point in the disease, the cancer has spread beyond the prostate gland. It might reach the outer layer of the prostate gland and spread to the seminal vesicles. Furthermore, in the IIIB stage, the cancerous cells might spread to organs like the bladder, rectum, and other nearby organs. If the cancer is at the IIIC stage, then the cells are poorly-differentiated.
• Stage IV
  Stage IV is the last stage of prostate cancer. Here, the cancerous cells have spread beyond the prostate gland. If it is at the IVA stage, the cancer has moved to distant lymph nodes. And if it is at the IVB stage, cancer has reached organs like lungs, brain, bones, among other organs.