Tumor CTR1 and serum copper dynamics reveal a coordinated copper axis linked to high-grade triple-negative breast cancer biology

Purpose: Copper is an essential trace element implicated in angiogenesis, tumor metabolism, and therapeutic resistance, yet its dynamic behavior during systemic treatment of breast cancer (BC) remains poorly characterized. The purpose of this study was to evaluate longitudinal changes in circulating copper (ΔCopper) during neoadjuvant therapy and to determine whether copper transporter biology, specifically CTR1 expression, the primary high-affinity copper importer, is associated with treatment response across breast cancer subtypes. Experimental Procedures: In a prospective neoadjuvant cohort, paired plasma samples were collected before initiation of therapy and at completion of neoadjuvant treatment. Total serum copper levels were quantified, and ΔCopper was defined as the difference between post-treatment and pre-treatment concentrations. Treatment response was assessed using standard pathologic criteria. To complement systemic measurements, a retrospective transcriptomic analyses of pretreatment tissue from 1,632 breast cancer patients were performed to evaluate CTR1 expression. System operating features were used to assess the ability of CTR1 expression to discriminate responders from non-responders. Results: We observed distinct, subtype-specific copper dynamics during neoadjuvant therapy in the prospective cohort. Non-responders, particularly within the triple-negative BC subtype, demonstrated a pronounced increase in ΔCopper compared with responders, suggesting heightened systemic copper mobilization in resistant disease. In contrast, hormone-receptor-positive tumors exhibited more modest copper fluctuations. Transcriptomic analyses revealed that elevated CTR1 expression was significantly associated with lack of response in aggressive subtypes, with improved discriminatory performance in triple-negative disease. Importantly, systemic ΔCopper and tumor CTR1 expression appeared biologically concordant, supporting a model in which resistant tumors exhibit increased copper demand, reflected both at the cellular transporter level and systemically in the circulation. Conclusions: These findings provide the first prospective evidence that dynamic changes in circulating copper during neoadjuvant therapy are associated with treatment response and align with copper transporter biology in BC. ΔCopper emerges as a promising, minimally invasive biomarker of copper-dependent therapeutic resistance, particularly in triple-negative BC. Together, these data support further investigation of copper metabolism as a predictive biomarker and therapeutic vulnerability, and they establish a rational for paired biospecimen analyses in the neoadjuvant setting to capture treatment-induced metabolic adaptations. Dartmouth-Health.org Dartmouth Cancer CenterOne Medical Center Drive, Lebanon, NH 03756