Kristy A. Brown

Background: The role of systemic inflammation in postmenopausal breast carcinogenesis remains unclear. Using a case-cohort study within the Melbourne Collaborative Cohort Study, we estimated the effects of circulating inflammatory biomarkers on the risk of postmenopausal oestrogen receptor (ER)-positive breast cancer. Methods: We included 1223 females (347 cases) who were postmenopausal at blood collection. For each biomarker, risk ratios (RRs) and 95% confidence intervals (CIs) for ER-positive breast cancer were estimated (1) per-doubling in biomarker concentration and (2) for quartiles of concentration with the lowest category as the reference, using weighted Poisson regression with a robust variance estimator. Results: The risk of postmenopausal ER-positive breast cancer increased per doubling in blood concentrations of leptin (RR: 1.13, 95% CI: 1.03, 1.25), adiponectin (RR: 1.10, 95% CI: 0.90, 1.34), tumour necrosis factor-alpha (RR: 1.27, 95% CI: 0.96, 1.68), and interleukin-10 (RR: 1.14, 95% CI: 1.01, 1.29). The RR for a doubling of the leptin-to-adiponectin ratio was 1.07 (0.99, 1.16). RRs for other biomarkers were 1.04 (0.93, 1.17) for interferon-gamma, 1.01 (0.88, 1.17) for interleukin-6, 0.98 (0.83, 1.16) for interleukin-8, and 1.03 (0.95, 1.11) for C-reactive protein. Conclusion: Systemic inflammation may be important in the risk of developing ER-positive breast cancer for postmenopausal females.

Background G protein-coupled receptors (GPCRs) are the largest class of membrane-bound receptors and are emerging as targets for the effective treatment of cancer. The role of orphan GPCR GPR52 in cancer has not been characterized. Low mRNA expression of GPR52 in breast tumours correlates with reduced overall survival, leading to the hypothesis that loss of GPR52 supports breast cancer progression. Methods CRISPR-Cas9 was used to knock out GPR52 in the human triple-negative breast cancer cell lines MDA-MB-468 and MDA-MB-231. 2D and 3D in vitro studies, electron microscopy, and a zebrafish xenograft model were used to assess the morphology and behaviour of GPR52 KO cells. Results Loss of GPR52 was associated with elevated levels of cAMP, increased cell–cell interaction in 2D cultures, more spindle-like morphology on collagen, altered 3D spheroid morphology, and increased propensity to organize and invade collectively. Zebrafish injected with GPR52 KO cells developed a greater total cancer area than control. RNA sequencing and proteomic analyses of GPR52-null cells revealed an increased cAMP signalling signature. Re-expression of GPR52 and inhibition of cAMP production rescued some GPR52 KO phenotypes. Conclusions GPR52 loss is a potential mechanism by which breast cancer progression may occur and supports the investigation of GPR52 agonism as a therapeutic option for breast cancer. Statement of Significance Loss of the orphan GPCR GPR52 in human breast cell lines leads to increased cell clustering, hybrid/partial EMT, and increased tumour burden in zebrafish, further expanding our understanding of mechanisms driving cancer progression and opening the door to novel therapeutic approaches.

Background: Adiposity increases the risk of post-menopausal oestrogen receptor (ER)-positive breast cancer. Inflammation, insulin, and insulin-like growth factors and sex-steroid hormones may explain this effect. We performed interventional mediation analysis to estimate the effects of hypothetical interventions targeting these pathways in females with obesity on reducing their excess risk of post-menopausal ER-positive breast cancer relative to females with normal weight. Methods: The mediation analysis included 1260 post-menopausal females (352 with ER-positive breast cancer) from a case–cohort within the Melbourne Collaborative Cohort Study. A Monte Carlo g-computation approach with non-parametric bootstrapping was used to estimate the risk differences (RDs) and 95% confidence intervals (CIs) for interventional direct and indirect effects of hypothetical interventions that shift the joint distribution of inflammation, insulin, and sex-steroid hormone biomarkers in females with obesity to the levels observed in females with normal weight. Results: The estimated RD for the total effect of obesity relative to normal weight on post-menopausal ER-positive breast cancer was 16.1 (95% CI: 3.3, 30.4) per 1000 females. The RDs for indirect effects through inflammation, insulin, and sex-steroid hormones were 16.4 (95% CI: 4.3, 27.2), −8.4 (95% CI: −23.4, 1.2), and 13.0 (95% CI: 3.3, 23.7) per 1000 females, respectively. The − RD for the direct effect not via any of these three pathways was −5.3 (95% CI: −17.4, 10.6) per 1000 females. Conclusion: Inflammation and sex-steroid hormones, but not insulin, contributed to the detrimental effect of adiposity on the risk of post-menopausal ER-positive breast cancer. Interventions targeting these pathways may reduce the risk for females with obesity.

Summary: Carrying a germline mutation in BRCA1 is associated with an increased risk of several cancers, including breast and ovarian. Our recent work has demonstrated that obesity is associated with elevated levels of DNA damage in breast glands in this high-risk population. BRCA1 is a canonical tumor suppressor gene primarily recognized for its role in DNA damage repair, yet emerging evidence suggests broader functions in metabolic regulation. To determine whether heterozygous loss of Brca1 , as seen in individuals who carry a germline mutation, modifies susceptibility to diet-induced metabolic dysfunction in a sex-dependent manner, we subjected wild-type (WT) and Brca1 ^+/− mice of both sexes to a high-fat diet (HFD) and performed longitudinal metabolic phenotyping. Female Brca1 ^+/− mice exhibited pronounced obesity, increased adiposity, hyperinsulinemia, and impaired glucose tolerance. In contrast, male Brca1 ^+/− mice showed modest resistance to HFD-induced weight gain and displayed improved glucose tolerance compared to WT controls. Notably, Brca1 heterozygosity led to more severe hepatic steatosis with HFD, indicating a shared susceptibility to liver lipid accumulation despite divergent systemic outcomes. In females, steatosis was associated with reduced mitochondrial respiratory complex IV activity and transcriptional remodeling that favored lipid storage. Treatment with the dual GLP⍰1/GIP receptor agonist tirzepatide ameliorated systemic metabolic dysfunction and hepatic steatosis in HFD–fed female Brca1 ^+/− mice. These findings identify Brca1 heterozygosity as a modifier of metabolic disease risk, expanding BRCA1 biology beyond tumor suppression. Abstract Figure:

Supplementary Figure 4 presents funnel plots for physical activity to inflammatory biomarkers meta-analyses

Supplementary Table 4 presents the outcomes of the meta-regression analysis conducted for CRP

Supplementary Table 6B presents findings of individual randomised cross-over studies

Supplementary Table 3 presents the risk of bias assessment, using the ROBINS-E

Supplementary Figure 2C presents the funnel plot from the meta-analysis of TNF-alpha and breast cancer risk

Supplementary Figure 1A presents forest plots for physical activity and CRP, by menopausal status