The invention relates to new compounds for cancer therapy or diagnosis and to the use of a non-toxic B subunit of Shiga toxin mutant as a vector for diagnostic products or drugs in over-expressing Gb3 receptor cells, such compounds having the following formula: STxB-Z(n)-Cys-Y(m)-T wherein-STxB is the Shiga Toxin B subunit or a functional equivalent thereof, -Z(n) wherein n is 0 or 1, Z is an amino-acid residue devoid of sulfydryl groups, or is a polypeptide, -T is a molecule linked by a covalent bound to the S part of Cys, selected from: agents for in vivo diagnosis, cytotoxic agents, prodrugs, or enzymes for the conversion of a prodrug to a drug, - Y(m) wherein m is 0 or 1, Y is a linker between T and Cys, which is either cleavable or not cleavable for the release of T after the internalization of the hybrid compound into cells.