IIB-BR-G is an undifferentiated, highly heterogeneous,
hormone receptor negative human
breast cancer cell line previously established in our laboratory from a patient's primary
tumor. An in vitro growing cell line (IIB-BR-G) and a xenotransplanted
tumor growing in nude mice (IIB-BR-G(NUDE)) were derived. To further characterize these systems, immunocytochemical analysis was performed for
differentiation antigens (PEM 200 kDa, CEA, NCA 90 kDa),
blood-group related
antigens (Le(x), sTn), oncogenes and tumor suppressor gene products (Her-2/neu
protein, p53),
metastasis-related
cathepsin D and CD63/5.01 Ag, and the
chemokine monocyte chemotactic protein 1 (MCP-1). Expression of markers was heterogeneous in these different systems. Previously reported karyotypic analysis has shown extensive chromosomal alterations including double min. Searching for oncogene amplification, we detected augmented copy number of c-myc and c-fos, the last one with two rearranged fragments. No amplification was found for c-erbB-2 in the cell line or in IIB-BR-G(NUDE), although this oncogene was amplified in the patient's primary
tumor DNA. The differences observed between the patient's
tumor, the cell line and the IIB-BR-G(NUDE)
tumors are probably due to clonal expansion of cell variants not present in the original
tumor. Electron microscopy of IIB-BR-G growing cells revealed epithelial characteristics with abundant dense granules, presumably secretory, distributed all over the cytoplasm and great nuclear pleomorphism. In vitro, IIB-BR-G cells showed a significant number of invading cells by
Matrigel assay. After nearly 40 sequential subcutaneous passages of the original xenograft through nude mice, 80% of recipients developed spontaneous
metastases, primarily to the lung and lymph nodes. Since this experimental model allowed to analyze changes produced in
cancer cells from the primary
tumor during adaptation to in vitro and in vivo growth, our results provide novel insights on the behaviour of
hormone independent metastatic
breast cancer.