BACKGROUND: Lymph node count (LNC) from neck dissection has been associated with undernutrition and survival in head and neck squamous cell carcinoma (HNSCC). As local components of the immune system, cervical lymph nodes may reflect anti-tumor immune status. This study investigates the relationship between decreased LNC, formation of tertiary lymphoid structures (TLS), and primary tumor infiltration by lymphocytes in undernourished patients. METHODS: A matched-cohort study was conducted in a tertiary medical center, where neck dissection quality was standardized for a total of 384 subjects that were evaluated. Six head and neck cancer patients that underwent primary surgery including neck dissection with low LNC and BMI (low BMI <
23, low LNC ≤ 5.6 per neck level) were matched by stage, p16 status, and subsite to 16 patients with normal BMI and high LNC. Multiplexed immunohistochemistry was used to evaluate the tumor-infiltrating lymphocytes and the number and quality of TLS within primary tumors. Whole primary cancers underwent automated analysis and counting of leukocytes after multiplexed immunohistochemistry staining of tumor slides. A head and neck pathologist blindly scored the number and maturity of TLS. Descriptive statistics were used to analyze outcomes. RESULTS: The patients with low BMI and low LNC had significantly fewer CD3 (p = 0.0136), CD8 (p = 0.0003), and CD20 (p = 0.0334) cells in their primary tumors compared to patients with normal BMI and LNC. The low BMI low LNC patients also had fewer mature TLS (0.83/tumor) in their primary cancers compared to patients with normal BMI and high LNC (5.4/tumor) and also had greater than fourfold lower mature TLS density (TLS per μm CONCLUSION: Low LNC predicts worsened survival only in low BMI HNSCC patients with non-HPV related tumors and in these patients is associated with markers of immunosuppression such as fewer tumor-infiltrating CD8+ T-cells, CD20+ cells, and fewer TLS in primary cancers compared to matched normal BMI patients with high LNC.