Carcinomas arising in the fundus of the uterus commonly contain cells that repeat essentially the characteristics of the lining columnar epithelium, in varying degrees of differentiation. Where the differentiation of the cells has occurred to a marked degree, there are present gland-like or papillary structures. However, there are other varieties of fundic carcinomas in which the cell arrangement differs, in that along with the columnar epithelium there are present masses of cells having the appearance of squamous cells. In fact, some tumors seem to consist only of such squamous epithelium, stratified in layers as in the epidermis, and containing masses of these cells in varying degrees of hornification. At present, the origin of the squamous cells is regarded as a metaplasia, but such an explanation regarding them has not always been the one offered or accepted.
Probably the first record of squamous cells in adenocarcinoma of the uterus was made
HIRSCH EF. STRATIFIED SQUAMOUS CELL CARCINOMA OF THE BODY OF THE UTERUS. Arch Surg. 1925;11(6):957-964. doi:10.1001/archsurg.1925.01120180150009