Disclosed is the use of an immunoconjugate in the manufacture of a medicament for treating a patient with a disease associated with target tumor cells expressing CD138, wherein the immunoconjugate comprises: at least one targeting antibody targeting CD138 expressing cells, and at least one effector molecule, wherein said targeting antibody is functionally attached to said effector molecule to form said immunoconjugate, wherein the targeting antibody comprises a heavy chain and a light chain, wherein the heavy chain comprises a CDR1 comprising NYWIE, CDR2 comprising ILPGTGRTIYNEKFKGKA and CDR3 comprising RDYYGNFYYAMDY, wherein the light chain comprises CDR1 comprising HSASQGINNYLN, CDR2 comprising YTSTLQS and CDR3 comprising QQYSKLPRT, wherein the targeting antibody comprises an IgG4 isotype constant region or part of the targeting antibody confers IgG4 isotype properties. Further disclosed is the use of an immunoconjugate in the manufacture of a medicament for treating a patient with a solid tumor comprising cells expressing CD138, wherein the immunoconjugate comprises: at least one targeting antibody targeting CD138 expressing cells, and at least one effector molecule, wherein said targeting antibody is functionally attached to said effector molecule to form said immunoconjugate, wherein the targeting antibody comprises a heavy chain and a light chain, wherein the heavy chain has SEQ ID NO: 1, and the light chain has SEQ ID NO: 2, and wherein the at least one effector molecule is a maytansinoid.
