Is upper lip cancer "true" lip cancer?

A description is given of the occurrence of upper and lower lip cancers in Finland in the period 1953-1974 with the aim of reaching conclusions on the possible differences in the etiological factors involved. Substantial differences with respect to various epidemiological parameters, such as incidence rates, trends in the incidence with time, male/female ratios of the incidence rates, age-incidence curves, urban/rural ratios of the incidence rates, and geographical distribution, were demonstrated between upper and lower lip cancers. On the other hand, similarities in the occurrence of upp]er lip cancer and non-melanomatous skin cancer of the head and neck could be observed. It was concluded that in terms of etiology upper lip cancer could be regarded as a separate entity and different from "true" lip cancer of the lower lip. The role of recurrent herpetic infections of the lips is also discussed.