As well as tyrosine kinase and mTOR inhibitors, new anticancer therapies make use of antibodies targeting tyrosine kinase receptors or blocking anti-tumor immune response checkpoints. These are always monoclonal; in their international non-proprietary names, the origin is prefixed to “-mab”: e.g., mouse antibodies end in “o-mab”, chimeric antibodies in “xi-mab”, humanized antibodies in “zu-mab” and human antibodies in “u-mab”. When the analytic principle of the assay involves a murine monoclonal antibody and the therapeutic antibody contains a murine sequence, analytic interference is to be feared if the patient develops antibodies against the therapeutic antibody. The interfering heterophilic antibody may be a HAMA (anti-mouse), a HACA (anti-chimeric) or a HAHA (anti-humanized-antibody). In immunoassay for patients under immunotherapy, it is therefore recommended to check the type of therapeutic antibody: if it is liable to contain murine sequences, heterophilic antibodies should be screened for and neutralized.