Abstract NG06: Investigating biological mediators of social and environmental risk factors on cancer health disparities
Authors: Lord Brittany D. , Rossi Emily , Dorsey Tiffany H. , Pichardo Catherine , Wooten William , Pichardo Margaret , Hutchison Ruby , Bailey-Whyte Maeve , Ajao Anuoluwapo , Ambs Stefan 
Published: April 2023

Background: Chronic life stress is more prevalent in low socioeconomic status (SES) communities and has been shown to affect DNA methylation and the immune system. Yet, the biological processes that mediate the impact of SES on health to promote the development of chronic diseases like cancer remain poorly understood. Previous studies have shown that individuals from disadvantaged neighborhoods experience a disproportionate amount of both chemical and non-chemical stressors, in addition to epigenetic alterations such as histone modifications and aberrant DNA methylation, compared to those from advantaged neighborhoods. These alternations lead to differential epigenomic profiles between these socioeconomic groups which can be long lasting, even transgenerational. Our study aims to uncover if DNA methylation is linked to neighborhood socioeconomic deprivation and to a biology that causes changes to the immune microenvironment that would promote breast cancer development, progression, and reduced survival. We are specifically interested in this relationship among Black and White women with breast cancer, largely due to the 40% increased mortality that Black women experience compared to White women.

Methods: DNA was extracted from 426 fresh frozen breast tissue samples from 173 Black and 116 White women in the NCI-Maryland Breast Cancer Cohort, including 185 tumor samples, 137 paired adjacent normal tissue samples, and 104 normal breast tissue samples collected from reduction mammoplasty. Using zip codes, we geocoded the locations of our study participants and linked these data to Census tract-level socioeconomic deprivation from the 2000 Census using a Neighborhood Deprivation Index (NDI). We conducted a principal component analysis (PCA) to extract a single variable that represented the shared variance across the original 20 deprivation indicators. PCA loadings about 0.25 were retained in our index including % of households in poverty, % of households on public assistance, % of households with no car, % of female headed households with dependent children, % of households earning less than $30,000 per year, and the % of males and females unemployed. Higher NDI values represented greater deprivation and lower NDI values correlated with less deprivation. The NDI was analyzed either on a continuous scale, in quartiles, or was dichotomized into high and low groups based on median cutoffs. DNA methylation data was acquired using the Illumina EPIC 850K array and a differentially methylated probe (DMP) analysis was done between tumor and paired adjacent normal tissue to identify gene regions of hypo- or hyper-methylation stratified by high and low NDI status. Additionally, using a volcano plot investigating fold change differences between NDI high and NDI low methylation beta values, we identified CpG methylation probes significantly associated with high NDI status in the tumor tissue. Finally, we used a methylCIBERSORT deconvolution analysis to estimate immune cell subpopulation differences by tissue type, race, and neighborhood deprivation status.

Results: In characterizing NDI by demographic and clinical characteristics in our cohort, we found that Black participants had significantly higher NDI levels compared to White participants (p&lt;0.0001) in both normal and tumor tissue. When considering tumor grade and molecular breast cancer subtypes, we found that higher tumor grade was significantly associated with high NDI status (p=0.0344), and higher mean NDI levels were observed in individuals with triple negative breast cancer as compared to hormone receptor positive breast cancer. From the DMP tumor versus adjacent normal paired analysis, we observed that the high neighborhood deprivation group showed more significant methylation events than the low neighborhood deprivation group, including increased hypo- and hyper-methylation in the tumor tissue compared to the adjacent normal tissue. We also found that the location of methylation changes were similar between the NDI high and low groups, with most occurring in the gene body and intergenic regions. In tumor tissue, we identified 8 hypo-methylated CpG probes that were significantly associated with high NDI status, including decreased methylation in the gene body region of two tumor suppressor genes, LRIG1 and WWOX. As methylation in the gene body of cancer cells often correlates to decreased gene expression, our results would indicate less transcriptional activity of these tumor suppressor genes in the NDI high group, potentially resulting in an increased risk of breast cancer metastasis, worse prognosis, and higher mortality. Finally, our methylCIBERSORT analysis showed decreased neutrophils in the NDI high group, which may correlate to poor response to neoadjuvant chemotherapy and more advanced stages of breast cancer.

Significance: To date, little is known about how the epigenome translates neighborhood disadvantage into health disparities. Our findings show evidence of differential methylation expression in tumor and adjacent normal tissue for individuals experiencing high neighborhood deprivation, potentially translating to more adverse breast cancer outcomes for this group. This work gives mechanistic insight into how socioeconomic position may affect cancerous mammary gland biology by altering DNA methylation patterns and immune cell responses.

Citation Format: Brittany D. Lord, Emily Rossi, Tiffany H. Dorsey, Catherine Pichardo, William Wooten, Margaret Pichardo, Ruby Hutchison, Maeve Bailey-Whyte, Anuoluwapo Ajao, Stefan Ambs. Investigating biological mediators of social and environmental risk factors on cancer health disparities. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG06.