Most head and neck cancers are known as squamous cell carcinomas, which originate in the flat squamous cells that form a thin, protective layer on the surfaces of organs in the head and neck region. Beneath this layer is the epithelium, which includes the mucosa—a moist tissue lining found in various parts of the head and neck.

When cancer extends beyond the squamous cell layer and invades deeper tissues, it is classified as invasive squamous cell carcinoma. These malignant tumors can develop in areas such as the mouth, nose, sinuses, throat, or jawline. Though they begin in the squamous cells, they often progress to form tumors that affect the surface and deeper tissues of organs in the head and neck.