Adenoid cystic carcinoma: A type of cancer that most often develops in the salivary glands of the head and neck. It may arise in other sites such as the skin, lacrimal gland, trachea, breast, cervix and prostate. Adenoid cystic carcinoma (ACC) has a characteristic appearance under the microscope. Abnormal "nests" or cords of certain cells (epithelial cells) can be seen to surround or infiltrate ducts and glandular structures. These structures are typically filled with a mucous-like material or contain abnormal fibrous membranes (hyaline membranes).
ACC is an unusual tumor. It is slow-growing but relentless. It tends to be locally invasive and infiltrate the "sheaths" or coatings surrounding nerve fibers (perineural spaces). ACC often recurs years later at the site where the tumor first arose or it may metastasize. Unlike most carcinomas, it seldom metastasizes to nearby lymph nodes but rather to distant sites. The lung is the most common site of metastasis, with the liver second. Bone metastases indicate a poor prognosis .
Treatment usually involves surgery to resect (remove) the tumor. Postoperative radiotherapy may help prevent local recurrence. Chemotherapy may slow the tumor but no chemotherapy has yet been found that is effective in destroying it.