The most common type of lip cancer is classified as squamous cell carcinoma, according to the National Cancer Institute. These cancers are a subtype of skin cancer that arise from the thin, flat cells that form the outer lining of the lips.
Not all lip cancers arise from squamous cells, as reported by the Skin Cancer Foundation. Some lip cancers are basal cell carcinomas that arise from cells deeper in the structure of the lip. Estimates from patient populations find that basal cell carcinomas account for only 28 percent of lip cancers, however. Risk factors for lip cancer include sun exposure, a weakened immune system, and heavy alcohol or tobacco use.