The present invention is related with the obtaining of modified antibodies by means of the DNA recombinant technology from the murine monoclonal antibody P3 (MAb P3) produced by the hybridoma cell line deposited under Budapest Treaty with accession number ECACC 94113026 and from its anti-idiotype murine monoclonal antibody 1E10 (MAbai 1E10) produced by the hybridoma cell line with deposit number ECACC 97112901, with the objective of achieving monoclonal antibodies which preserve the biological function of specific binding to the antigen of the original antibodies, but being at the same time less immunogenic. The chimeric antibodies of the invention contain the variable domains of the murine immunoglobulin and the constant regions of the human immunoglobulin; and those humanized, besides containing the constant regions of the human immunoglobulins, they are modified in the region of the murine frameworks (FRs) and in particular in those zones that could be in an antigenic site for the T cells, so several positions of the FRS are human as well. These antibodies can be used in the diagnosis and therapy of different types of tumors. The present invention is also related with use of the antibodies for therapeutical and diagnostic purposes.