by Jason Wasserman MD PhD FRCPC
May 26, 2022
A carcinoid tumourlet is a group of neuroendocrine cells in the lung that measures less than 5 millimeters in size. In addition to the size, a group of neuroendocrine cells can only be called a tumourlet if the cells do not show any abnormal features such as an increased number of mitotic figures (cells dividing to create new cells) or a type of cell death called necrosis.
Neuroendocrine cells are specialized cells that are normally found in the walls of the airways throughout the lungs. Most pathologists consider carcinoid tumourlets to be a non-cancerous overgrowth of neuroendocrine cells and not a type of cancer. Carcinoid tumourlets are often found incidentally when lung tissue is removed for another reason.