Extranodal extension is a term pathologists use to describe a group of cancer cells in a lymph node that have broken through the capsule and spread into the surrounding tissue. Some pathologists use the term extracapsular extension to describe the same features.
A lymph node is a small organ filled with specialized immune cells. It is part of the body’s immune system. A capsule is a thin tissue barrier on the outside of the lymph node. The capsule separates the lymph node from the surrounding tissues and organs.
Metastasis is a group of cancer cells that have travelled from the original tumour to another area of the body such as a lymph node. For this reason, pathologists examine lymph nodes to look for cancer cells. This allows them to determine the nodal part (pN) of the pathologic cancer stage (pTNM). Extranodal extension is important because for some types of cancer it increases the pathologic nodal stage and is associated with a higher risk that the cancer cells will spread to other parts of the body.