Re‐exploring immune‐related side effects of docetaxel in an observational study: Blood hypereosinophilia

Docetaxel is a major anticancer drug that can induce hypersensitivity reactions leading to deleterious treatment interruptions. Blood hypereosinophilia could be a biological sign, potentially lethal, of delayed visceral hypersensitivity reactions. We hypothesized this biological event is probably underreported. In this prospective observational study, we followed up 149 patients treated with docetaxel monotherapy for breast or lung cancer. For each patient, blood eosinophil counts were recorded during docetaxel treatment and up to 3 months after the end of docetaxel treatment. For all patients, blood eosinophil counts significantly increased under docetaxel chemotherapy (P < 0.01). Seven percent had persistent eosinophilia after the end of treatment. Four patients had blood eosinophil counts over 1000/mm(3) with severe cardiac, cutaneous and digestive toxicities, and docetaxel imputability was confirmed using drug‐imputability scales. For two of these four patients, tissue biopsies were performed during the time of hypereosinophilia and of severe toxicities. Specific immunostainings and electron microscopy found numerous degranulating mast cells and eosinophils. Our study demonstrated that eosinophilia is frequent under docetaxel and could lead to severe complications, implicating eosinophils and mast cells, and possibly IgE. One way of treating hypersensitivity reactions could be by targeting IgEs with omalizumab, an anti‐IgE monoclonal antibody approved for the treatment of severe allergic asthma, and successfully used in food and poison‐induced anaphylactic reactions.