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. Pathologists use the term extranodal extension (ENE) 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.
The spread of cancer cells from the original tumour to a lymph node or other part of the body is called metastasis. Pathologists carefully examine all lymph nodes removed with a tumour to look for metastasis and this information is used 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 worse prognosis.