Abstract LB-219: Higher levels of mast cells associate with favorable outcomes in non-small cell lung cancer and correlate with lower malignant cell proliferation
Authors: Gentles Andrew J. , Hui Angela , Feng Weiguo , Nair Ramesh V. , Yu Alice , Shafiq Majid , Forgo Erna , Khuong Amanda , Xu Yue , Hoang Chuong D. , West Robert B. , Rijn Matt van de , Diehn Maximilian , Plevritis Sylvia K. 
Published: July 2017

Abstract
The tumor microenvironment (TME) involves complex interactions between malignant and stromal cell types. Much of our knowledge of cancer biology has been derived from studying molecular mechanisms underlying bulk tumors, with a focus on specific malignant pathways that have become dysregulated during tumorigenesis and tumor progression. Although studies have identified interactions between malignant and stromal cells within the TME, few have sought to comprehensively identify such relationships. Here, we performed RNA-seq on bulk and flow-sorted non-small cell primary human lung tumors enriching for malignant cells, endothelial cells, immune cells, and fibroblasts. We derived a map of cell-specific differential gene expression of prognostically associated secreted factors and cell surface markers, and computationally reconstructed pairwise cross-talk between cell types. We found significant novel associations between transcriptional profiles of malignant populations and specific stromal populations, focusing here on mast cells.
We identified presence of infiltrating mast cells to be negatively correlated with malignant cell proliferation. Expression of TPSAB1 (Tryptase Alpha/Beta 1) is largely confined to mast cells, and its high expression in both adenocarcinoma and squamous cell carcinoma is favorably prognostic in both histologies across multiple datasets based on gene expression data. We validated the prognostic relevance of mast cells in NSCLC by immunohistochemical (IHC) staining of a lung tumor tissue microarray (TMA) for MCT (mast cell tryptase). Higher mast cell count was associated with better overall survival across all NSCLC, or when considering either adenocarcinoma or squamous cell carcinoma alone. When mast cell counts were quantified as “High”, “Intermediate”, “Low”, and “Negative” levels without reference to clinical outcomes, these were statistically significantly associated with survival. Negative-, low-, and intermediate-levels of mast cells all conferred worse prognosis than high mast-cell levels. Mast cell levels remained prognostic in multivariate analysis with independent clinical factors including age, stage, and gender. Finally, we directly evaluated the relationship of mast cell levels to tumor proliferation by staining the same samples for the proliferation marker KI67. The percentage of tumor cells staining positive for KI67 was lower in tumors with high vs low numbers of mast cells (p=0.048, Wilcox rank-sum test).
In summary, we identified and validated a specific inverse relationship between levels of infiltrating mast cells and malignant cell proliferation. These results illustrate the utility of transcriptomic profiling of flow-sorted subpopulations from solid tumors in order to identify tumor-microenvironment interactions that may have prognostic and therapeutic relevance.
Citation Format: Andrew J. Gentles, Angela Hui, Weiguo Feng, Ramesh V. Nair, Alice Yu, Majid Shafiq, Erna Forgo, Amanda Khuong, Yue Xu, Chuong D. Hoang, Robert B. West, Matt van de Rijn, Maximilian Diehn, Sylvia K. Plevritis. Higher levels of mast cells associate with favorable outcomes in non-small cell lung cancer and correlate with lower malignant cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-219. doi:10.1158/1538-7445.AM2017-LB-219