Histological studies of the mode of origin of tumors

All of the tubular adenocarcinomas of early gastric cancer in humans showed gentle transitions from surrounding normal to neoplastic epithelium. In mammary carcinomas in C3H/He mice, known as viral tumors, there were also transitional appearances from normal to cancer cells. Furthermore, it was possible in rats to trace gradations between normal fibrocytes and sarcoma cells in marginal areas of tumors induced subcutaneously by 3-methylcholanthrene (MCA). It cannot be explained by the mutation of a few somatic cells that transitions from normal to neoplastic cells were observed not only in viral tumors in mice but also in human carcinomas and in chemically induced tumors in rats. It seems well to think of the mode of origin of all types of tumors as an excessive cellular regeneration to make up for the functional disturbance of cells invaded by oncogenic viruses.