Immune infiltration at the primary tumor is associated with clinical outcome of patients with extranodal extension of lymph node metastasis in oral cancer

Background Extranodal extension (ENE) of lymph node metastasis is one of the most reliable prognostic indicators for patients with locally advanced oral cancer. Although multiple reports have found a close relationship between immune infiltration of tumors and patient clinical outcomes, its association with ENE is unknown. Methods We identified 234 human papillomavirus-negative (HPV−) oral cavity squamous cell carcinoma (OSCC) patients in The Cancer Genome Atlas and investigated the immune infiltration profiles of primary tumors and their association with survival. Results Hierarchical clustering analysis clearly classified the overall immune infiltration status in OSCC into high immune or low immune groups. The combination of ENE positivity and low immune infiltration was strongly associated with poor overall survival (OS) compared to the combination of ENE positivity and high immune infiltration [hazard ratio 2.04 (95 %CI, 1.08–3.83); p = 0.024]. The immune infiltration status was not associated with OS rates in patients with ENE-negative or node negative tumors. Conclusion Overall Immune infiltration at the primary site was significantly associated with clinical outcome of OSCC patients with ENE.