Oral carcinoma in situ. Its progression to squamous, basosquamous, and basal-cell carcinoma

We studied a tumor of the oral mucosa that initially appeared as an intraepithelial carcinoma, and then progressed after one year to invasive squamous carcinoma and after eight years to basal-cell carcinoma (BCC) with admixture of basosquamous and squamous carcinomas. This tumor, which originated from basal cells, reflects the ability of these cells to produce neoplasms that range from those consisting of least-mature elements (basal cells) to mature ones (squamous cells), with intermediary types that contain both elements (basosquamous carcinoma). These transformations imply that BCCs can arise from the basal layer of skin and oral mucosa and that the terms BCC, basosquamous carcinoma, and squamous carcinoma are descriptive rather than of histogenetic significance.