The present invention relates to a monoclonal antibody binding to the LG4/5 domain of chain alpha3 of human protein laminin-5, wherein said monoclonal antibody inhibits the binding of syndecan-1 to said laminin-5 alpha3 chain LG4/5 domain, in particular 1H12 monoclonal antibody produced by the hybridoma cell line named 1H12 deposited on January 8, 2008 at the C. N. C. M. under number 1-3890, as well as chimerized, humanized derivatives and fragments thereof, and nucleic acid sequences encoding them, as well as vectors and host cells expressing them. The invention further relates to the medical application of such antibodies, in particular for treating cancer.