AbstractBackgroundSeveral studies describe an inverse statistical relationship between the presence of an allergy and development of cancer. However, the immunological mechanism involved in the relationship between these two degenerative diseases has not been explored.AimsThe main objective of this study was to explore the possibility that the lymphocyte T helper (Th) 2 response, a characteristic of allergy, induces recognition of tumor antigens.Methods and resultsPatients with a clinical diagnosis of breast ductal carcinoma were included. Histopathological markers related to proliferation of tumor cells were determined (Her‐2‐neu, Ki‐67, estrogen receptor, and progesterone receptor). IHC was performed using IgE antibodies purified from an allergy patient and from each biopsy donor patient. Serum concentrations of cytokines representative of Th1 and Th2 inflammatory responses were determined. A total of 14 patients with a confirmed diagnosis of breast ductal carcinoma were included. IHC performed on biopsies showed a weak response when using purified IgE antibodies from an allergy patient; however, IHC using the IgE of each patient as the primary antibody showed an intense and highly specific signal. Serum concentrations of cytokines of the Th2 response, that is, IL‐4 (130.5 pg/mL (116–135 pg/mL)), IL‐5 (202 pg/mL (191–213 pg/mL)), and IL‐13 (105.5 pg/mL (98–117 pg/mL)), were significantly higher than those of the Th1 response, that is, IL‐6 (86 pg/mL (79–90 pg/mL)) and INF‐γ (93 pg/mL (79–99 pg/mL)).ConclusionPurified IgE antibodies specifically recognize tumor cells in breast ductal carcinoma.