Anti-HER2/neu, anti-EGFR, anti-CD20, anti-folate receptor alpha (FRα) IgE and anti-prostate specific antigen (PSA) IgE antibodies were all able to trigger rat basophil leukaemia (RBL) SX-38 mast cell degranulation when cross-linked in different ways including soluble antigen/polyclonal antibody complexes, cancer cells expressing multiple copies of the target antigen, and polyclonal anti-IgE. The gene discussed is ERBB2; the disease is cancer.