The floor of the mouth is a “u” shaped area located between the mandibles; posterior to the lingual-palatal arch, medial to the ventral side of the tongue, and lateral and anterior to the medial side of the mandible. The carcinoma of the floor of the mouth refers to the squamous cell carcinoma of the mucous membrane of the floor of the mouth, and those who like to chew betel nut and tobacco are prone to develop carcinoma of the floor of the mouth. Causes 1. Long-term addiction to tobacco, alcohol and betel nut chewing Most patients with fundus cancer have a long-term history of smoking and alcohol consumption, while those who do not smoke and drink alcohol are rare. In some regions of the world, such as Sri Lanka, India, Burma, Malaysia and other places, residents have the habit of chewing betel nut or “Naas”. Chewing betel nut and other mixtures can cause the oral mucosa epithelial basal cell division activity increase, so that the incidence of fundic cancer increases. Keller data in the United States shows that the incidence of cancer of the floor of the mouth in smokers who do not drink alcohol or alcoholics who do not smoke is 2.43 times and 2.33 times, respectively, while the incidence of those who have a habit of smoking and drinking is 15.5 times that of those who do not smoke or drink. Alcohol itself has not been shown to be carcinogenic, but it has a pro-carcinogenic effect. Alcohol may act as a solvent for carcinogens and promote carcinogens to enter the oral mucosa. 2, poor oral hygiene Poor oral hygiene habits create conditions for bacteria or mold to breed and multiply in the oral cavity, thus facilitating the formation of nitrosamines and their precursors. Coupled with stomatitis, some cells are in proliferative state and more sensitive to carcinogens, so all these reasons may promote the occurrence of carcinoma in the floor of mouth. 3.Long-term stimulation of foreign body Dental roots or sharp tooth tips, unsuitable dentures stimulate oral mucosa for a long time, resulting in chronic ulcers and even cancer. Some people think that it is related to the lack of vitamin A, because vitamin A has the function of maintaining the normal structure and function of epithelium, and the lack of vitamin A can cause the thickening and hyperkeratosis of oral mucosa epithelium, which is related to the occurrence of fundic carcinoma. Demographic studies have shown that countries with low vitamin A intake have a high incidence of fundic carcinoma. Vitamin C deficiency has not yet been shown to be associated with fundic carcinoma. It is also thought to be related to insufficient intake of micronutrients, such as low iron content in food. Insufficient intake of total protein and animal protein may be associated with fundic carcinoma. Zinc is an indispensable element for the growth of animal tissues, and zinc deficiency may lead to mucosal epithelial damage, creating favorable conditions for the development of fundic carcinoma. Clinical manifestations Mostly occurring on both sides of the tongue ligament, early manifestations are small hard nodules or erythema, later developing into ulcers. The lesion easily invades to the contralateral floor of the mouth, gingiva, lingual bone plate of mandible and lingual ventral muscle, causing destruction of mandibular bone, loosening of mandibular teeth and restriction of tongue movement. At this time, patients have obvious symptoms such as pain, salivation and difficulty in eating. Submandibular gland enlargement and pain are often seen when submandibular gland ducts are invaded by floor of mouth cancer. The carcinoma of the floor of the mouth that occurs in the posterior floor of the mouth is likely to invade the mandible and tongue belly at an early stage. Lymph node metastasis: The rate of regional lymph node metastasis is high, about 35% to 70%, mostly bilateral. The most easily involved lymph nodes are subchin and submandibular lymph nodes, which may metastasize to deep upper cervical lymph nodes. If the lesion is less than 1cm in extent and the infiltration thickness is less than 2.0mm, local enlargement resection is feasible. If the tumor invades the mandible or has metastasis to the cervical lymph nodes, combined radical surgery of fundic lesion, mandible and cervical lymph should be performed. The tissue defect after resection should be repaired at the same time. For early stage anterior fundic carcinoma, bilateral suprascapular hyoid lymph node dissection should be performed; for those with primary origin in posterior fundus, cervical lymph node dissection should be performed. Radical cervical lymph node dissection should be performed if there are lymph node metastases.