Noninvasive precursor lesions of adenocarcinoma and mixed adenosquamous carcinoma of the cervix uteri.

It is postulated that squamous cell carcinoma, adenocarcinoma, and mixed adenosquamous cell carcinoma of the uterine cervix all have a common cell or origin, the subcolumnar reserve cell. The relative frequency with which the various types of carcinoma in situ are seen is in part explained by the ubiquitous nature of squamous metaplasia in the region of the transformation zone in women of reproductive age. It is suggested that squamous metaplasia is the soil on which most squamous carcinomas of the cervix evolve. The relatively low frequency with which adenocarcinoma and adenosquamous carcinoma in situ are encountered may also be dependent on their less accessible location in the endocervix.