The immunomodulatory impacts of endocrine therapy on host immunity in early-stage hormone receptor positive, HER2 negative breast cancer.
Authors: Sammons Sarah L. , Dent Susan Faye , Chang Ching-Yi , Liu Siyao , Chan Isaac , Weinhold Kent J. , Perou Charles M. , McDonnell Donald P. 
Published: May 2024

572 Background: Endocrine therapy (ET) reduces mortality in hormonally driven breast cancer (BC). The impacts of ET on the estrogen receptor are well known; however, there is limited data on the impact of ET on the host's immune system. This project aims to elucidate the potential immunomodulatory effects of ET-induced estrogen deprivation in HR+/HER2 negative early-stage breast cancer patients (pts) as well as baseline differences between BC pts and healthy controls (HC). Methods: Pts with Stage I-III HR+/HER2- BC initiating ET after completion of local regional therapy and/or chemotherapy were enrolled (NCT03719495). Whole blood, E1 (estrone) and E2 (estradiol) levels were collected at baseline (T1), 4 weeks (T2), 12 weeks (T3) and 24 weeks (T4) after ET initiation. 5 cohorts were enrolled: premenopausal and postmenopausal HCs, premenopausal pts on tamoxifen (TAM) or aromatase inhibitors (AIs) plus ovarian suppression, postmenopausal pts on AIs. Bulk RNA sequencing of whole blood was performed using NuGEN mRNA-seq on the Illumina Nova-seq platform. Differential expression analysis was performed using DESeq2 between HC and ET groups at T1, and between T1 and T4 within BC pts. The Benjamini-Hochberg method was used to adjust the P values for multiple comparisons. A curated set of 192 immune related gene signatures was used in the gene signature analysis. For each signature/module, a score was computed by taking the median of the expression values from all genes in each gene signature. CIBERSORT analysis was performed using the LM22 signature gene file and 100 permutations. Paired t-test was performed to compare T1 and T4. Results: Between 2019 and 2023, 64 pts were enrolled. Pts with missing samples or prior chemotherapy were excluded in this analysis. T1 samples of 25 pts with BC versus 14 HCs revealed marked changes in circulating immune cell (IC) composition with 537 DEGs (p value < 0.05). Circulating ICs in BC pts had marked upregulation of genes associated with oxidative phosphorylation, adipogenesis, interferon alpha, reactive oxygen species compared to HCs. Immune cell composition was inferred by CIBERSORT analysis which suggests that BC pts had fewer circulating naïve B cells (p=0.048) whereas regulatory T cells (p=0.025) and activated NK cells (p=0.0039) were higher in BC pts than HCs at T1. BC pts with reductions in E1/E2 levels 6 months after ET had 77 DEGs in PBMCs between T1 and T4. Gene signature analysis shows that B cells and NK cells (p=0.0077) signatures are elevated post ET whereas a reduction of neutrophil signature (p=0.0034) was noted. Conclusions: There are significant differences in the baseline IC repertoire/activity in BC pts compared to HCs. The reduction in B cell activity/number and an increase in regulatory T cell number suggests a possible compromised immune system in BC pts. After surgery and 6 months of ET, these suppressed immune phenotypes reversed. Clinical trial information: NCT03719495 .