Understanding the TNM Prostate Cancer Staging System

Understanding the TNM Prostate Cancer Staging System

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.

The TNM clinical stage is a sophisticated method of predicting the probability that a prostate tumor is confined to the prostate or has spread beyond the gland. Here’s a description of this important staging system:

T1: Tumor cannot be felt during DRE or seen with diagnostic imaging

  • T1a: Tumor found incidentally during surgery for benign prostatic hyperplasia (BPH) and is present in less than 5 percent of removed tissue
  • T1b: Tumor found incidentally during BPH surgery but involves more than 5 percent 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

    TNM Information from The Johns Hopkins Medical Center