Low Mast Cell Density Predicts Poor Prognosis in Oral Squamous Cell Carcinoma and Reduces Survival in Head and Neck Squamous Cell Carcinoma

Background: The cellular composition of the tumor microenvironment (TME) at the invading front of oral squamous cell carcinomas (OSCCs) may reflect biologically important cancer features and host responses, and thus be related to disease progression. The TME density of mast cells (MCs), macrophages, cancer-associated fibroblasts (CAFs) and endothelial cells were quantified at the invasive front and analyzed regarding their relation to disease recurrence in patients with small T1/2N0M0 OSCCs. mRNA for MC-specific proteins were analyzed in a second patient cohort with head and neck squamous cell carcinoma (HNSCC). Materials and Methods: Samples from 62 patients with T1/2N0M0 OSCC were immunohistochemically stained and scored for the cellular expression of mast/stem cell growth factor receptor (c-KIT) (MCs), CD68 (macrophages), a-smooth muscle actin (a-SMA) (CAFs) and CD31 (endothelial cells) and this was analyzed according to disease recurrence. Data from The Cancer Genome Atlas database were used to examine mRNA expression profiles and clinical data of patients with 399 HNSCC. Results: Increased MC density at the invasive front was significantly associated with reduced disease recurrence, as none of the patients with high MC density experienced relapse. Moreover, increased expression of mRNA for MC specific markers as c-KIT, and alpha-, beta-, and delta-tryptases and the MC-stimulating factor, stem cell factor (SCF), was significantly associated with good prognosis in patients with HNSCC. Conclusion: Decreased MC density at the invasive front may reflect tumor biology related to disease progression and prognosis. Counting MCs seems to be an easy and practical tool, that could be utilized for prognostic evaluation.