Loss of Plexin-B1 expression is associated with poor prognosis in melanoma (22) and estrogen receptor–positive breast cancer (23) but is a favorable prognostic factor for ErbB2-amplified breast cancer (24) and ovarian cancer (25) suggesting that Plexin-B1 can act as a tumor suppressor or an oncogene depending on context. This evidence concerns the gene ERBB2 and breast cancer.