Tumor staging is a way to classify the size and spread of a tumor. Staging primarily focuses on the size of the tumor and if it has spread to the nearby lymph nodes. To determine a cancer’s stage, the TNM system is most commonly used. The T refers to the primary tumor, the N refers to the regional lymph nodes, and the M refers to the metastasis (or spread to distant sites).[1] Lymph node involvement is an important measure of cancer spread because cancer cells that have broken off from the primary tumor either travel through the bloodstream or the lymph system. For the cancer cells that travel through the lymph system, they often end up in the lymph nodes. If cancer is found in the lymph nodes, it is more likely to continue spreading to other locations.[2] The TNM staging system will be described:

This TNM classification is general, and different types of cancer have their own specific version of the TNM categories. For some types of cancer, there can also be subcategories such as T3b. Additionally, some types of cancer will have less categories (such as no N3 category).[1]

Once values for T, N, and M are assigned, the overall tumor stage can be determined. Stages usually range from I to IV, with I being the least severe and IV being the most severe. Some types of cancer also have a stage 0 which is referred to as in situ.1 Stage IV means the cancer has metastasized.[3] Stages also may be further subdivided by adding a letter after the number, such as Stage IIB.[1]

References:

1.     Cancer Staging https://www.cancer.org/treatment/understanding-your-diagnosis/staging.html (accessed Jun 10, 2021).

2.     Lymph Nodes and Cancer https://www.cancer.org/cancer/cancer-basics/lymph-nodes-and-cancer.html (accessed May 4, 2021).

3.     Cancer Staging https://www.cancer.gov/about-cancer/diagnosis-staging/staging (accessed Jun 10, 2021).