Abstract P5-03-02: Adiposity and immune-related gene expression in the breast tumor microenvironment
Authors: Dillon Deborah A. , Feliciano Elizabeth M. Cespedes , Zimbalist Alexa , Cheng En , Caan Bette J. , Chen Wendy Y. , Mittendorf Elizabeth A. , Peixoto Roberto Bonfim Pimenta , Domingos Tabata Alves , Taneja Krishan , Patel Ashka 
Published: March 2023

Background: Extreme adiposity has been associated with tumor progression and increased mortality after a breast cancer diagnosis, but the underlying mechanisms remain unclear. Pre-clinical and in vitro analyses suggest that higher levels of adiposity impair anti-tumor immunity, but studies in human breast cancer patients are lacking. Previously, we found that higher levels of subcutaneous adiposity had stronger associations with breast cancer outcomes than did higher levels of visceral adiposity or overall obesity measured by BMI, underscoring the importance of measuring adipose tissue distribution as well as overall body size to understand the adiposity-cancer link.

Methods: We identified women with a first-primary, stage 2 or 3 invasive breast cancer diagnosed and treated at Kaiser Permanente Northern California between 2005 and 2015. Using diagnostic computed tomography scans collected as part of routine clinical care, we measured subcutaneous (SAT) and visceral adipose tissue (VAT) areas in cm2 at the third lumbar vertebra. We calculated body mass index (BMI) from clinically-collected height and weight. We isolated RNA from 251 FFPE breast tumors collected at biopsy or excision; these were a preliminary, random sample within each immunohistochemical subtype groups from an ongoing study that will analyze 1400 breast tumors. We verified RNA quality prior to performing NanoString BC 360™ assays to calculate the PAM50 molecular intrinsic subtype and measure the expression levels of genes related to immune cell abundance and anti-tumor immune activity. Using linear regression models, we examined the mean change in log2 gene expression (dependent variables) associated with each adiposity exposure (BMI, SAT and VAT as independent variables).

Results: Mean (SD) age at diagnosis was 56 (13); a majority of women were either overweight (BMI 25- &lt; 30-kg/m2: 30%) or obese (BMI&gt;30-kg/m2: 35%), and most were diagnosed with stage 2 (61%) vs. stage 3 (39%) breast cancer with representation from each PAM50 subtype: n (%) Luminal A, 46 (18%) Luminal B, 56 (22%), HER2-overexpressing 26 (27%), and 82 (33%) basal-like. In unadjusted analyses, expression of genes related to macrophages, PD-1 and TIGIT increased with increasing subcutaneous adiposity, whereas expression of genes related to mast cells decreased (see Table 1). We found a similar (though non-significant) pattern for BMI. Associations with increasing visceral adiposity were closer to the null. After adjusting for PAM50 subtype, age and stage at diagnosis, only the association of increasing subcutaneous adiposity with increasing PD-1 expression remained statistically significant.

Conclusion: Excess subcutaneous adiposity was associated with increased PD-1 expression, whereas excess visceral adiposity or obesity defined by BMI were not. These results from the first 251 samples of an ongoing study of 1400 tumors provide evidence from human breast cancer patients to demonstrate the importance of measuring body composition to assess adipose tissue distribution and support the hypothesis that excess adiposity impairs anti-tumor immunity.

Association of Adiposity Measures with Immune-Related Gene Expression in the Breast Tumor Microenvironment (n=251 patients with stage 2-3 breast cancer at Kaiser Permanente Northern California) 195% Confidence Interval 2A 1-unit increase represents a doubling in the log expression level of the genes in the signature

Citation Format: Deborah A. Dillon, Elizabeth M. Cespedes Feliciano, Alexa Zimbalist, En Cheng, Bette J. Caan, Wendy Y. Chen, Elizabeth A. Mittendorf, Roberto Bonfim Pimenta Peixoto, Tabata Alves Domingos, Krishan Taneja, Ashka Patel. Adiposity and immune-related gene expression in the breast tumor microenvironment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-03-02.