Tumour-associated tissue eosinophilia (TATE) in oral squamous cell carcinoma: a comprehensive review

Oral squamous cell carcinoma is the most common head and neck malignancy, characterised by high invasive capacity, lymph node metastasis, and high recurrence rate. Among the morphological features of oral cancer, the tumour-associated tissue eosinophilia has gained growing interest in the last years. Eosinophils are a minor subpopulation of leukocytes, representing 1-3% of all circulating white blood cells. The presence of high levels of eosinophils is associated with several diseases, but their role in cancer pathophysiology is controversial. In particular, an uncertain and contradictory relationship exists between the exact role of tumour-associated tissue eosinophilia and oral cancer development. Many studies have shown that tumour-associated tissue eosinophilia increases both in the progression of oral potentially malignant disorders as well as in the grade and stage progression of oral cancer. Despite this, both negative and positive prognostic outcomes have been associated with eosinophil infiltration. The heterogeneous results may be partially due both to several methodological inconsistencies and to an incorrect interpretation of the physiological role of eosinophils. Therefore, further studies to elucidate the contribution of eosinophil infiltration are needed, focusing on the existence of eosinophil subpopulations regulated by the cancer immune microenvironment. Furthermore, the correct reporting of prognostic marker research is encouraged, in order to ensure the reproducibility and the comparability of the results from different studies.