Transplantation of a cell line derived from a canine benign mixed mammary tumour into nude mice.

The MCM-B2 canine mammary cell line was serially transplanted into nude mice. The tumour masses consisted of elongated pleomorphic cells of varying size in the first to third passages; oval cells, becoming rounder, in the sixth to eighth passages; and cord-like, glandular and duct-like structures with compact radiating projections in the ninth and tenth passages. Ultrastructural and immunohistochemical examination of round cells confirmed their epithelial cell nature, but the morphology of the elongated and oval cells was identical with that of the original cell line. The findings suggest that the MCM-B2 cell line is a multipotential stem cell or is derived from glandular differentiation of mammary gland.