Pale cell carcinoma: ultrastructure of a hormone-dependent mammary tumor in GR mice.

Pale cell carcinoma, a hormone-dependent mammary tumor in GR mice, consists mostly of islands of pale cells and dark cells, interrupted by a few areas containing keratinized cells. In this study the pale cells (electron-lucent), were arranged in bands adjacent to vascular spaces, while the dark cells, which produced mammary tumor virus, were clustered around lumens. A morphometric analysis revealed that pale cells were larger than dark cells and had other differences that indicated they were swollen. The areas having keratinized cells (or cells displaying squamous cell differentiation) resulted from a transformation of certain pale cells, perhaps in response to injury. The cells developed large desmosomes, accumulated tonofilaments, and sometimes displayed keratohyalin granules; and although most pale cells did not fully keratinize, a few did. Moreover, they remained within pale cell carcinomas that had regressed.