Disclosed is an antibody or an antigen binding portion thereof that specifically binds to BST1, said antibody comprising: a) a heavy chain variable region comprising: i) a first vhCDR comprising GYSFIEYTINW； ii) a second vhCDR comprising a sequence selected from the group consisting of GNIDPYYGTTYYNQMFT and NIDPYYGTTYYNQMFQ； and iii) a third vhCDR comprising ARGSAWFPY； and b) a light chain variable region comprising: i) a first vlCDR comprising SASSSVTYMY； ii) a second vlCDR comprising DTSNLAS； and iii) a third vlCDR comprising QQWSNYPLT. Also disclosed is the use of the above-described antibody or an antigen-binding portion thereof in the manufacture of a medicament for the treatment of cancer wherein the antibody or antigen-binding portion thereof is internalised by a cell expressing BST1, said antibody comprising a covalently attached drug conjugate.
