Electron microscopic studies on transplantable mucus-secreting and tubular adenocarcinomas of colo-rectal origin in ACI/N rats.

Two transplantable, one mucus-producing (R-1) and the other tubular but less mucinous (R-2), adenocarcinomas were investigated electron microscopically. The R-1 tumor was composed of a large number of intermediate cells and mucus-producing cells, incompletely differentiated goblet-like cells and absorptive-like cells, and a small number of undifferentiated cells. The electron microscopic features of the mucus-producing cells exhibited distinctive features different from those of the epithelium of normal colon. They had highly electron-dense granules, expanded rER, well-developed mitochondria and Golgi apparatus. The R-1 tumor was found to be a well-differentiated adenocarcinoma in agreement with observations by light microscopy, while the R-2 tumor exhibited more malignant features than R-1.