The present invention relates to certain anti-M(H)DM2/4 antibodies or antigen- binding fragments thereof, pharmaceutical compositions comprising anti-M(H)DM2/4 antibodies or antigen-binding fragments thereof, antibody-drug conjugates comprising anti-M(H)DM2/4 antibodies or antigen-binding fragments thereof bound to a cytotoxic drug, and the use of such antibodies, fragments, compositions and conjugates for treating cancer and/or for preventing metastases. In particular, described herein are certain antibodies or antigen-binding fragments thereof that specifically bind to extracellularly accessible epitopes of M(H)DM2/4 and inhibit tumor growth
