Allergooncology: an expanding research area

The relationship between allergic diseases and cancer is a very controversial topic, widely discussed in the last decades. Many studies have demonstrated inverse association between allergy and cancer, but others have reached neutral conclusions or have indicated a positive role of allergy in the development of cancer. However, either inhibiting or favoring, many cells and molecules relevant in the allergic process play a role in tumorigenesis. On the one hand, activated immune cells, like classically activated macrophages "M1", activated dendritic cells, IL-33 and amphiregulin stimulated Innate Lymphoid Cells (ILC2), Th1, IFN-γ producing T CD8+ and B lymphocytes have inhibitory effects on tumorigenesis and tumor progression. On the other hand, tolerogenic immune cells, like alternatively activated macrophages "M2" (M2a, M2b and M2c), tolerogenic dendritic cells, ILC3, T regulatory and B regulatory lymphocytes, while inhibiting allergic sensitization and response, appear to favour carcinogenesis. Furthermore, M2 subtypes macrophages (M2a, M2b), IL-25 stimulated ILC2 and Th2 lymphocytes have a role both in inducing allergic reactions and in favouring cancer progression. In addition, mast cells, pivotal cells in allergy, have a different effect of tumorigenesis based on their location - they can promote cancer progression or inhibit it. Finally, eosinophils have shown a prevalent tumoricidal function mediated by α-defensins, TNF-α, granzymes A and IL-18. Better understanding the role of various cells on carcinogenesis can help in developing new strategies (diagnostic, therapeutic and of follow up) against tumor.