Abstract PS18-50: Single-cell transcriptomic analysis reveals tumor microenvironment in male breast cancer
Authors: Sun Handong , Wang Zhonglin , Zhu Yanhui , Yang Chuang , Wang Qianghu , Wei Jifu , Ding Qiang 
Published: February 2021

Objectives: Male breast cancer (MBC) is a rare aggressive malignant tumor that accounts for only 1% of all breast cancers and has a worse prognosis compared with female breast cancer (FBC). However, little is unveiled regarding the mechanisms of MBC occurrence and development, and there is a lack of relevant basic research and clinical studies at a global scale. The rapid development of single-cell transcriptomic technologies has helped uncover the heterogeneity within cell populations and tumor microenvironment, as well as the clonal evolution of breast cancer cells. This study aims to explore: (1) the tumor microenvironment of MBC; (2) the heterogeneity of male/female breast cancer cells and cell subgroup differences; (3) the potential specific therapeutic targets and biological characteristics differences between MBC and FBC.

Methods: Single-cell transcriptome sequencing (scRNA-seq) and single cell sequencing of T cell receptors (scTCR-seq) combined with whole genome sequencing (WGS) and immunohistochemical staining were performed to deeply analysis the heterogeneity and clonal evolution of MBC, reveal the tumor microenvironment, especially the composition and function of tumor infiltrating immune cells. We performed scRNA-seq using fresh samples from three luminal type MBC patients and two post-menopausal luminal type FBC patients. Firstly, t-SNE dimensionality reduction analysis was conducted according to different genders, different patients and subpopulation of cells, and gene expression profiles were processed and visualized using heatmap. Moreover, through comprehensive analysis of scRNA-seq and scTCR-seq results of MBC and FBC, we further explored the characteristics, interrelation and dynamic changes of various types of cells in the tumor interior, and then mined novel specific therapeutic targets.

Results: Based on the single cell sequencing results, we observed a striking difference in cell subsets distribution and gene expression profiles between MBC and FBC. The cell subsets were then sorted by the proportion of MBC tumor cells, and 7 subsets were selected as potential MBC specific cellular subpopulation. Further comparative analysis with Luminal type of post-menopausal FBC samples suggested that fatty acid synthase (FASN) expression was remarkably elevated in MBC, and the overall survival was significantly decreased in MBC patients with high FASN expression. Meanwhile, MBC tumors were found to have lower rates of immune cell infiltration and higher proportion of exhausted T cells, which were also validated by immunohistochemical staining of 160 cases of pathological sections. Surprisingly, we also observed the presence of some “intermediate cells”only in MBC specimens, which exhibited simultaneous expression of cancer epithelial cell marker KRT8 and T cell marker CD3E. These “intermediate cells”showed immunosuppressive status.

Conclusion: In this study, we found that the high expression of FASN and the lipid metabolism pathway may play important roles in the MBC development, providing theoretical foundation and experimental basis for further clinical trials of FASN inhibitors, as well as precision therapy and prognostic evaluation for MBC. Meanwhile, further study of the “intermediate cells” may facilitate the discovery of novel tumor immune escape strategies. Our findings also played a role in promoting the comprehensive description of tumor microenvironment of MBC and the mechanism study of its occurrence and development.

Key words: male breast cancer, single-cell sequencing, tumor microenvironment, intermediate cells, fatty acid synthase

Citation Format: Handong Sun, Zhonglin Wang, Yanhui Zhu, Chuang Yang, Qianghu Wang, Jifu Wei, Qiang Ding. Single-cell transcriptomic analysis reveals tumor microenvironment in male breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-50.