The present invention relates to a conjugate comprising an anti-EGFR1 antibody or an EGFR binding fragment thereof and at least one dextran derivative, wherein the dextran derivative comprises at least one D-glucopyranosyl unit, wherein at least one carbon selected from carbon 2, 3 or 4 of the at least one D-glucopyranosyl unit is substituted by a substituent of the formula —O—(CH2)n—S—B12H112− wherein n is in the range of 3 to 10； and the dextran derivative is bound to the anti-EGFR antibody or an EGFR1 binding fragment thereof via a bond formed by a reaction between at least one aldehyde group formed by oxidative cleavage of a D-glucopyranosyl unit of the dextran derivative and an amino group of the anti-EGFR1 antibody or an EGFR1 binding fragment thereof.
