Diagnosis
If a screening test or symptoms suggest prostate cancer, the next step is usually a prostate biopsy. A biopsy is a procedure in which small samples of prostate tissue are removed (using a thin, hollow needle) and examined under a microscope for cancer cells. This is the only way to definitively diagnose prostate cancer. Most often, a transrectal ultrasound (TRUS) or MRI is used to guide the biopsy needle into the prostate through the rectal wall, although biopsies can also be done through the perineum (the skin between the scrotum and anus). Typically, about 10–12 tissue cores are taken from different parts of the prostate. The procedure is brief and done with local anesthesia to minimize discomfort. After a biopsy, a pathologist will determine if cancer is present in the samples and, if so, how aggressive it appears.
Gleason Score / Grade Group: When cancer is found, the tumor cells are graded based on how abnormal they look. The most common grading system is the Gleason score, which ranges from 6 (least aggressive) to 10 (most aggressive) for prostate cancer. Pathologists actually assign two grades for the two most predominant patterns seen in the cells (each on a scale of 1 to 5) and add them – for example, a Gleason 7 could be 3+4 or 4+3, with the second pattern indicating a somewhat more aggressive tumor.
Today, doctors often simplify this into Grade Groups 1–5, where Grade Group 1 corresponds to Gleason 6 (low-grade), Grade Group 2 and 3 correspond to Gleason 7 (intermediate grades), Grade Group 4 is Gleason 8, and Grade Group 5 is Gleason 9–10 (high-grade). A lower Grade Group (1) means the cancer cells look relatively similar to normal and are likely to grow slowly, whereas a higher Grade Group (4 or 5) means the cells are very abnormal and the cancer may grow or spread quickly. The grade (along with PSA level and tumor extent) helps predict the cancer’s behavior and guide treatment decisions.
If a prostate biopsy confirms cancer, additional tests are done to determine the cancer’s stage (how far it has spread). This staging work-up may include imaging tests such as:
Magnetic resonance imaging (MRI): to visualize the prostate and see if the tumor extends outside the gland or into nearby structures.
Computed tomography (CT) scan or PET scan: to check lymph nodes or other organs. Newer PET scans (e.g. PSMA PET) can very sensitively detect prostate cancer spread. - Bone scan: because prostate cancer often spreads to bones, a bone scan can look for any metastatic lesions in the skeleton.
These tests show whether cancer is confined to the prostate or has spread to regional lymph nodes, bones, or other organs. The extent of spread (stage) is crucial for planning treatment. (For example, a small tumor only in the prostate might be cured with local therapy, while cancer that has spread will need systemic treatment.) Your doctor will discuss which tests are appropriate based on your PSA level, biopsy results, and any symptoms.
Staging and Grading
Staging describes how advanced the cancer is – essentially, how far it has spread in the body. Prostate cancer is typically assigned a stage from I (one) to IV (four), often using the TNM system (Tumor-Node-Metastasis) in combination with PSA and Grade Group. In general:
Stage I means a very early cancer that is localized – it’s small and confined within the prostate. Often, Stage I prostate cancers can’t even be felt on exam; they might have been found by needle biopsy due to a PSA test. The PSA is usually low and Grade Group 1 (low grade).
Stage II is also localized (no spread outside the prostate) but the tumor may be larger or detectable on one or both sides of the prostate. PSA levels are typically moderate, and Grade Groups can be 1–3 for Stage II. This stage indicates the cancer is still limited to the prostate gland but is perhaps more extensive than Stage I.
Stage III means locally advanced disease. The tumor has grown outside the prostate into nearby tissues. Stage IIIA/B indicates extension beyond the prostate capsule (for example into the seminal vesicles or surrounding tissue). Lymph nodes are not involved yet in Stage III. PSA may be high, and Grade Groups can vary up to 4 or 5 in some Stage III cases.
Stage IV is the most advanced. In Stage IVA, the cancer has spread to nearby lymph nodes in the pelvis. In Stage IVB, it has spread to distant sites such as bones, liver, or lungs (distant metastasis). Any spread to distant organs or bones is stage IV. At this stage, PSA can be any level and Grade can be any group; the key factor is that the cancer is no longer contained in the prostate region.
