SKBR3 are rarely used for xenograft s, and we haven't used these. BT474 has been used for xenograft s but doesn't produce spontaneous Mets in our experience. 21MT1, made by Dr Vimla Band (published 1989) are known to give Mets. Her lab recently generated metastatic ErbB2 expressing tumor cell lines by expressing an oncogene combination in immortal human mammary stem/progenitor cell lines. I am sure there are other lines. 4T1 mouse mammary tumor line is not ErbB2 positive.