SEMA4A and breast carcinoma: To elucidate the molecular mechanism by which PLXNB2 facilitates tumor cluster formation, we investigated whether in breast cancer PLXNB2 interacts with any of its canonical ligands on the cell surface, such as single-pass transmembrane proteins, semaphorin (Sema) family members SEMA4A, 4C, 4D, and 4G51,54,58–62.