Prostate Cancer

Staging

Prostate cancer is cancer that forms in tissues of the prostate, a walnut-sized gland in the male reproductive system. The prostate gland is located below the bladder and in front of the rectum. Prostate cancer is the most commonly diagnosed cancer in men and it occurs more frequently as age increases beyond 60 years.

The most widely employed staging system is the American Joint Committee on Cancer (AJCC) tumor, node, metastasis (TNM) classification; AJCC stage at diagnosis provides an approach to estimate the prognosis of a cancer since stage is an estimate of likelihood of spread. Other factors which influence the likelihood that the cancer has spread include the Gleason score and the prostate-specific antigen (PSA) level at diagnosis.

As a first step in identifying the stage of prostate cancer, the doctor who has evaluated the findings of diagnostic tests will assign a clinical stage. The clinical stage is defined on the basis of the findings on physical examination and the results of imaging studies, which usually include a bone scan and computerized tomography (CT) and rarely positron emission tomography (PET). These tests enable the doctor to estimate the size and location of the tumor (T category) and the absence or presence of cancer in nearby lymph nodes (N category) or other parts of the body (M category) (Table 1). Stage may be confirmed more precisely by a pathologist who examines tissue removed during surgery or biopsy. This final stage is called the pathologic stage.

The pathologist also assigns a Gleason score, which indicates the grade of the prostate tumor, or how similar the tumor tissue is to normal prostate tissue. The Gleason scoring system ranges from 2 to 10. A low score is given when the tumor looks more like normal prostate tissue, and higher scores are given when the cancer looks “less differentiated” or less like normal tissue.

The higher the Gleason score, the more likely the tumor is able to spread. Thus, a high Gleason score means that the tumor is aggressive, and the prognosis (predicted outcome) is relatively worse than for a tumor with a low Gleason score (a less aggressive tumor). This score is part of the staging process because it indicates how likely a tumor is to spread and has implications for treatment decision-making.

The preoperative PSA level is a factor in staging; generally speaking the level of serum PSA is a reflection of how much cancer there is and hence lower PSA level is associated with better survival outcomes.

The AJCC classification, Gleason score, and PSA level at diagnosis are then used to determine an overall stage of disease (Table 2). Some doctors may use an older staging system, the Whitmore-Jewett system, and assign stage A, B, C or D to the prostate cancer. Patients are encouraged to ask their doctors to explain the staging system they use or to translate the stage into a stage determined by the AJCC system, as the AJCC system has been shown to provide much more information on prognosis.

Table 1. American Joint Committee on Cancer (AJCC) System for Classifying Prostate Cancer

*When a tumor is found during surgery not related to prostate cancer, it is further classified as T1a if tumor cells are found in 5% or less of the surgically removed prostate tissue, and as T1b if tumor cells are found in more than 5% of the surgically removed prostate tissue. A tumor is classified as T1c if it is found during a needle biopsy, usually done because of an elevated prostate-specific antigen (PSA) level.

Table 2. Stage of Prostate Cancer According to AJCC Classification

*The prostate cancer is defined as stage I when the Gleason score and PSA level are not known for men who have a tumor with either of these TNM classifications.

?The prostate cancer is defined as stage IIA when the Gleason score and PSA level are not known for men who have a tumor with either of these TNM classifications.