Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

• Lips. The lips form the upper and lower anterior walls of the oral cavity. Each lip consists ofan exposed surface of modified epidermis known as the vermilion border and a labial mucosa*(mucous membrane) which lines the inner surface of the lip. Striated muscle and fibroelasticconnective tissue lie beneath the surface."Lip" should not be confused with "skin of lip" which is not part of the digestive system.The commissure is the point of union of the upper lip and the lower lip (corner of the mouth).Malignant TumorsThe lower lip is the most common site of malignancy in the oral cavity. Malignant tumors of theupper lip are relatively rare. The most common type of malignant tumor of the lip is squamous cell(epidermoid) carcinoma.Figure 22. LIPS__/._J/SkJ.n o:I _pper LipLowerLIp"--------Skin of Lower Lip*Note: The latest revisions of the American Joint Committee define the lip as the vermilion surfaceonly. The mucosa of the lip is included with the buccal mucosa. The ICD-O provides separate codenumbers for labial mucosa (C00.3, C00.4) and vermilion surface (C00.0, COO.I)of the lip. You cancombine or separate as you wish. Historically, the mucosa of the lip has been defined as part of thelip.170