There are several ways of categorizing prostate cancers. These include grading systems, which indicate the degree of abnormality in cells taken in a biopsy, and staging systems, which indicate how large a tumor is and how far it has spread.

The most common grading system used with prostate cancer is the Gleason grading system. It assigns a number to both of the biggest two areas of cancer in tissue samples extracted in a biopsy. One is least aggressive, and five is most aggressive. These two grades are added to create a Gleason score.

Gleason scores rate the seriousness of the threat posed by a tumor and predict how fast it might spread:

• Low grade: 2 to 4. Slow growing tumors that are least likely to pose a threat.
  
  
• Intermediate grade: 5 to 7. Cancer that has spread to other tissues (metastasis) and is relatively less common than high grade.
  
  
• High grade: 8 to 10. Metastasis of the cancer is common.

In addition to grading systems, prostate cancers are ranked according to several staging systems. The most commonly used is the TNM Staging System. It details the extent of the primary tumor, whether the cancer has spread to nearby lymph nodes, and whether there is metastasis to distant structures.

The combination of the grading system and staging system results in a four-stage system:

• Stage I. A localized prostate tumor that cannot be felt. Less than 5 percent of a tissue sample is cancerous.
  
  
• Stage II. A localized tumor that can be felt but is limited to the prostate.
  
  
• Stage III. A regional tumor that has grown through the prostate, possibly to the seminal vesicles.
  
  
• Stage IV. Metastatic tumors that have spread beyond the prostate and seminal vesicles.

There are also other types of staging systems, such as one that uses a ranking of A, B, C or D.

Below is the five-year survival rate (percentage of men who survive prostate cancer at least five years), according to the American Cancer Society: