Quantitative assessment of tumor-associated tissue eosinophilia and mast cells in tumor proper and lymph nodes of oral squamous cell carcinoma.

Background: Oral squamous cell carcinoma (OSCC) is the most common cancer of the oral cavity. Tumor stage, thickness, lymph node metastasis (LNM), extranodal spread, perineural invasion, tumor differentiation, mutations, human papillomavirus infection and tumor microenvironment are independent prognostic indicators of OSCC. However, clinically, among all factors, LNM is considered an important prognostic factor in OSCC as it not only determines the stage of disease but also the strongest independent factor which predicts recurrence of disease. Further research proves that there are several biologically important factors in tumor tissue and LNs which promote or defend LNM. While it is proposed that tumor-associated tissue eosinophils (TATE) and mast cells (MCs) have "immuno-protective" effect, this remains unproven and various researchers have conflicting opinion.

Aim: The aim is to determine the presence of TATE and MCs in OSCC and to evaluate if any association exists between them and LNM.

Study Design: It is a comparative retrospective study between two groups including 35 OSCC cases positive and 35 negative for LNM.

Materials and Methodology: Quantification of cells was done by counting total number of cells in 10 high-power fields under ×40 objective lens using "zigzag" method and dividing it by total number of fields. Eosinophils stained bright red with carbol chromotrope and MCs purple-violet with toluidine blue.

Statistics: Independent t -test and Pearson's correlation were done using STATA IC 0.2 software. The level of significance was at 5%. Comparison of eosinophil and MC infiltration was done based on gender, metastatic, nonmetastatic LN and in tumor proper.

Results and Conclusion: Our study showed weak positive correlation between mean eosinophils count in tumor and LNs which implies a definite association between the microenvironment of tumor, its progression and LNM. There was a significant association between MC density and decreased LNM also. We conclude that an increased number of immunological cells (TATE and MCs) are a favorable prognostic indicator in OSCC. There is evidence of reduction in LNM with increasing density of these immunological cells. Recognition of TATE and MCs as integral to tumor biology opens an avenue for novel approaches to cancer therapies.