Spatial distribution and prognostic value of tumor-associated macrophages in head and neck squamous cell carcinomas.

Introduction: Tumor-associated macrophages (TAMs) belong to the most frequent immune cells in the tumor microenvironment of head and neck squamous cell carcinomas (HNSCC). They can undergo an anti- or pro-tumoral polarization, the latter often referred to as M2-like activation. Because existing data are either not consistent, not well-connected to clinicopathological parameters or lack a detailed spatial distribution, we aimed to get more insight into the relevance of this immune cell population and their activation status. Methods: This study analyzed the spatial distribution and prognostic value of CD68+TAMs and CD68+CD163+M2-like TAMs in different tumor compartments and tumor-distant stromal areas, in 85 treatment-naïve HNSCC. Various clinicopathological features were considered, such as major tumor sites, stage, T-stage, nodal status and p16-status. TAM and M2-like TAM densities were analyzed using multicolor immunofluorescence stainings followed by an objective tissue cytometry-based quantification at the single-cell level in whole tissue sections and subsequent uni- and multivariate survival analyses. Results: Whereas we observed higher TAM and M2-like TAM densities in p16-negative HNSCC specimens, densities of M2-like TAMs were highest in the tumor-near stroma of advanced nodal-positive p16-negative HNSCC compared to tumor cell nests and tumor-distant stroma, particularly in younger and male patients and patients with hypopharynx carcinomas. Moreover, higher infiltration of M2-like TAMs turned out to be an independent prognostic factor of poorer survival even exceeding the impact of the p16-status and the tumor site. Discussion: In summary, our data provide a strong rationale to target M2-like TAMs to improve success of immune-modulatory treatments and survival of patients suffering from p16-negative HNSCC.