Adenoid cystic carcinoma is also known as cylindroma or cylindroma-type adenocarcinoma. Most people believe that the tumor arises from the ducts of the salivary glands and possibly from the basal cells of the oral mucosa. It most commonly occurs in the minor salivary glands of the palate and parotid glands, followed by the submandibular glands. Tumors that occur in the sublingual glands are mostly adenoid cystic carcinomas. Tumors tend to spread along the nerves and often present with neurological symptoms such as local pain, facial palsy, tongue numbness or sublingual nerve palsy. The tumor is extremely invasive and has no boundary with the surrounding tissues. The tumor is easy to invade blood vessels and the rate of metastasis to blood vessels is as high as 40%, and the most common site of metastasis is lung. The metastasis rate of lung is the most common site. The metastasis rate of cervical lymph nodes is low. In the early stage of tumor, painless mass is the most common, but in a few cases, pain is present at the time of detection, and the pain is intermittent or continuous. Some of the pain is mild and some can be severe. The duration of the disease is long, several months or years. The tumor is usually small, mostly 1 to 3 cm, but some are larger in size. The shape and characteristics of the mass may resemble a mixed tumor (see my article: Diagnosis and management of mixed tumors of the parotid gland). They are round or nodular and smooth. Most of the masses are not well defined and are poorly mobile, some are more fixed and have adhesions to surrounding tissues. Adenoid cystic carcinoma of the parotid gland has more chances of facial nerve palsy and may extend along the facial nerve and involve the mastoid process and temporal bone; adenoid cystic carcinoma of the submandibular or sublingual gland may extend along the lingual or sublingual nerve to a site far from the primary tumor and cause perceptual and motor impairment of the affected tongue; adenoid cystic carcinoma of the palate may extend along the maxillary nerve into the skull and destroy the skull base and cause severe pain. Adenoid cystic carcinoma of the palate can extend intracranially along the maxillary nerve and destroy the skull base and cause severe pain. The tumor also often invades adjacent bone tissue. Patients usually have no obvious systemic symptoms except for the complications in the late stage which make the disease deteriorate. Treatment is based on surgical resection. When designing the surgery, the normal boundary of the surgery should be expanded compared with other malignant tumors, and intraoperative frozen section examination should be performed to determine whether the surrounding tissues are normal. Postoperative radiotherapy is often required to kill the possible residual tumor cells. Chemotherapy can be used postoperatively to prevent hematologic metastasis. In principle, adenoid cystic carcinoma should be treated by total excision of parotid gland. Considering that adenoid cystic carcinoma is highly neuroinvasive, preservation of facial nerve should not be overly considered; for submandibular gland, at least submandibular triangle clearance should be performed; for those occurring in palate, submaxillary or total resection of maxilla should be considered. In addition to extensive resection, recurrent or advanced tumors can be treated with radiation therapy. In some anatomical areas where surgery is not complete, postoperative radiation therapy is also required. Surgery with radiation therapy may reduce the recurrence rate. For some cases where the chance of surgery is lost, radiation therapy can also be used to control the development. In the past, it was thought that malignant tumors of salivary gland were resistant to radiation, but some recent studies have shown that adenoid cystic carcinoma is sensitive to radiation, but radiotherapy alone cannot completely cure it.