Relationship of hyperplasia to cancer in 3-methylcholanthrene-induced mammary tumorogenesis.

Light microscopic study of the evolution of 3-methylcholanthrene-induced mammary tumors in Wistar-Furth rats revealed a seriation of changes proceeding from early hyperplasia (8 days) to advanced hyperplasia (57 days) and cancer (78 days). Ultrastructurally, cellular changes in advanced hyperplasia and cancer were indistinguishable, being characterized by nuclear chromatin clumping, prominent nucleoli, cytoplasmic polyribosomal aggregates and pseudopodal extensions, and prominent Golgi structures. These features, as well as the lack of limiting lamina basalia, allowed for their distinction from the cells of early hyperplasia. Further, only nodules of both advantanced hyperplasia and cancer were transplantable in syngeneic recipients. Chromosomal aberrations were qualitatively similar in cells obtained from all lesions but were progressively more frequent. Although these findings do not allow for the discrimination of advanced hyperplasia and cancer, they indicate their close pathogenetic relationship as well as the very early occurrence of chromosomal alterations in the development of mammary cancer in this model system.