Determining the extent of prostate cancer is important for predicting the course of the disease and in choosing the best treatment. The TNM (tumor, nodes, metastasis) staging system is used to describe a cancer's clinical stage, or how far it has spread. This Health Alert provides an explanation of this important prostate cancer staging system.
The TNM system assigns a T number (T1 to T4) to describe the extent of the tumor as felt during a digital rectal exam (DRE). The N number (N0 to N1) indicates whether the cancer has spread to any lymph nodes, and the M number (M0 to M1) indicates the presence or absence of metastasis (spread to distant sites). The T and M designations are divided into subcategories (designated a, b, and c) that provide further detail on the extent of the cancer.
- T1a: Tumor found incidentally during surgery for benign prostatic hyperplasia (BPH) and is present in less than 5% of removed tissue
- T1b: Tumor found incidentally during BPH surgery but involves more than 5% of removed tissue
- T1c: Tumor found during needle biopsy for elevated PSA
T2: Tumor can be felt during DRE but is believed to be confined to the gland
- T2a: Tumor involves one half or less of one side of the prostate
- T2b: Tumor involves more than one half of one side but not both sides
- T2c: Tumor involves both sides of the prostate
T3: Tumor extends through the prostate capsule and may involve the seminal vesicles
- T3a: Tumor extends through the capsule but does not involve the seminal vesicles
- T3b: Tumor has spread to the seminal vesicles
T4: Tumor has invaded adjacent structures (other than the seminal vesicles), such as the bladder neck, rectum, or pelvic wall
NO: Cancer has not spread to any lymph nodes
N1: Cancer has spread to one or more regional lymph nodes (nodes in the pelvic region)
MO: No distant metastasis
M1: Distant metastasis
- M1a: Cancer has spread to distant lymph nodes
- M1b: Cancer has spread to the bones
- M1c: Cancer has spread to other organs, with or without bone involvement
