Loss of production of myoepithelial cells and basement membrane proteins but retention of response to certain growth factors and hormones by a new malignant human breast cancer cell strain.

Digestion of primary breast cancers and their metastases with collagenase yields cell clusters which can be selectively isolated from stromal cells and from the less malignant-looking epithelium of the primary tumors by their failure to attach as rapidly to collagen gel. Continued passage in culture of one preparation of cell clusters has yielded a continuously growing cell strain, termed Ca2-83. This strain continues to grow mainly as cell clusters with doubling times of 10 to 14 days, although some clusters eventually adhere to plastic substrata. Two morphological extremes of cell were observed, smaller polygonal or cuboidal cells and larger, often-multinucleated cells which contain fat droplets. Cell clusters grew in a gland-like pattern similar to those of the original carcinoma and formed small nodules in 50% of recipient nu/nu mice. Both morphological forms of Ca2-83 in culture or in tumor nodules stained immunocytochemically with epithelial cell-specific antisera to epithelial membrane antigens and to human keratins but not to laminin or actin. Cultures of Ca2-83 failed to synthesize laminin under conditions where its synthesis was observed in a rat myoepithelial cell line. Ultrastructural analysis of the cell clusters has identified microvilli coated with epithelial membrane antigens and junctional complexes typical of secretory epithelia in both morphological forms, but no characteristics of myoepithelial cells or basement membranes were observed. The DNA content of the cultures increased in response to serum, a bovine pituitary fraction, and insulin. Numbers of cell clusters were also increased in the presence of culture medium exposed to preadipocytes, myoepithelial- or mesothelial-like cells/stromal cells, or to prostaglandin E2.