This invention relates to a composition of a non-labeled monoclonal antibody binding to a tumor antigen and a second monoclonal antibody labeled with a NIR fluorescence label, binding to the same tumor antigen, wherein the first and second antibody exhibit no cross reactivity. The composition can be used for the treatment of patients suffering of solid tumors which are associated with an overexpression of such a tumor antigen. The invention further relates to a the co-administration of said first and second antibody as wells as to a method of acquiring a NIR fluorescence images of such tumors or the patients suffering from such tumors during the treatment of said patient with such composition.