Anti-erbb2 antibody-drug conjugate and composition thereof, preparation method therefor, and use thereof

A method for the prophylaxis or treatment of cancer, comprising administering to a patient in need thereof an antibody-drug conjugate represented by Formula (I), or a pharmaceutically acceptable salt or stereoisomer thereof, or a solvate of the foregoing,

• wherein:
• A is an anti-ErbB2 antibody or an active fragment or variant thereof;
• X is N;
• Y is N or CR1, and R1 is H or C1-C10 alkyl;
• L is a divalent linker;
• D is a cytotoxic agent group;
• and
• a is an integer selected from the group consisting of 2-10;
• and
• all the cytotoxic agent groups are conjugated to the light chain of the antibody.