IL4 and neoplasm: High levels of Th2 cell-derived cytokines were detected in tumor sites of patients with breast cancer, with the levels of IL-4 and the amount of tumor-infiltrating CD4+ T cells being positively correlated with tumor progression, as well as with metastasis to sentinel lymph nodes,15,355,356 highlighting the clinical relevance of Th2 cells in the pathogenesis of breast tumors.