The invention provides anti-ETBR antibodies and immunoconjugates and methods of using the same. In some embodiments, an immunoconjugate comprising an antibody that binds ETBR covalently attached to a cytotoxic agent is provided, wherein the antibody binds an epitope within amino acids 64 to 101 of SEQ ID NO: 10. In some embodiments, the cytotoxic agent is a nemorubicin derivative.