The lip cancers refer to the cancers occurred in the lip vermilion mucosa (the exposed lip vermilion mucosa when the lips are naturally closed) and the joint mucosa in the corner of the mouth (within the range of 1 cm backward from the oral fissure). The cancers occurred in the inner side of the lip mucosa belong to the category of buccal mucosa carcinoma. The vast majority of cancers occurred in the lip vermilion mucosa are squamous cell carcinomas, and most of them are better differentiated; a small part of lip cancers are the basal cell carcinomas, which are caused due to the fact that the lip skin is invaded, and the adenocarcinoma is rarely seen.

The incidence of lip cancer is 1.8/100,000, accounting for 0.6% of the malignant tumors in the whole body and 9.57% of oral and maxillofacial squamous cell carcinoma. About 90% of lip cancers occur in the middle-aged and elderly people over the age of 40, more than half of them occur in the elderly people over the age of 60, and they occur more in men than women. More than 90% of lip cancers occur in the lower lip and occasionally occur in the upper lip. The lip cancers are more likely to occur in the mucosa of the prolabium at the junction of the middle and outer one third of the lower lip, and it is occasionally observed that the lip cancer occurs in the corner of the mouth. Most of lip cancers are solitary, and they have a slow disease progression and a longer disease course of usually 6 months to more than a year. The early lesions are presented as small herpes, induration, uncured chronic ulceration, or limited thickening and hardening of lip vermilion mucosa; the lesion is slowly increased and extended to the lip lump protruding outwardly or the deeper ulcer with a slightly elevated edge; the patients often have no self-conscious symptom and occasionally have mild pain and a little bleeding. Later on, the lesions are extended to the surrounding mucosa and skins, and the deep muscles are violated, and the cauliflower-like mass with edge eversion or crater-like ulcer is formed; the mass surface is covered with a gray-black eschar; the surface is presented as uneven small nodular shape. After the eschar is removed, the erosive wound and a little bleeding can be observed; the pain often occurs and is gradually aggravated. In the advanced stage, the lesion can be spread to the most part of the lip and even the whole lip, buccal cavity, and mandible, and the salivation, eating disorders, and more severe pain will occur [1, 2].

The blood supply of the lip comes, respectively, from the superior and inferior labial arteries and the branch of the facial artery, the labial arteries surround the mouth to form an arterial arch, and, therefore, the lesion in the one side of the lip is supplied with blood by the blood vessel from the middle part and one side of the lip. The sensations in the skin around the lip and at the junction of the skin and mucous membrane are controlled by the branches of the maxillary and mandibular divisions of trigeminal nerve. The movements of the orbicularis oris muscle and the muscle above and under the corner of the mouth are dominated by the branches of the facial nerve.

The lymphatic drainage of the lip has a certain direction; firstly the lymphatic fluid of the lower lip is drained into the lymph nodes in front of the facial blood vessel on the surface of the mandible and the level I lymph nodes and then is drained into level II and III lymph nodes; therefore, the level IV and V lymph node metastases are very rarely seen in the patients with lip cancers. The hematogenous distant organ metastases are rarely seen in the patients with lip cancers [3, 4].