Environmental factors play a role in breast cancer development. While metals and metalloids (MMs) include some carcinogens, their association with breast cancer depends on the element studied. Most studies focus on individual MMs, but the combined effects of metal mixtures remain unclear. The aim of this study was to analyze the relationship between the joint exposure to MMs and the risk of developing female breast cancer. We conducted a case-control study within the multicenter prospective EPIC-Spain cohort. Study population comprised 292 incident cases and 286 controls. Plasma concentrations of 16 MMs were quantified at recruitment. Potential confounders were collected using a questionnaire and anthropometric measurements. Mixed-effects logistic regression models were built to explore the effect of individual MMs. Quantile-based g computation models were applied to identify the main mixture components and to estimate the joint effect of the metal mixture. The geometric means were highest for Cu (845.6 ng/ml) and Zn (604.8 ng/ml). Cases had significantly higher Cu concentrations (p = 0.010) and significantly lower Zn concentrations (p < 0.001). Cu (+0.42) and Mn (+0.13) showed the highest positive weights, whereas Zn (−0.61) and W (−0.16) showed the highest negative weights. The joint effect of the metal mixture was estimated at an OR = 4.51 (95%CI = 2.32–8.79), suggesting a dose-response relationship. No evidence of non-linearity or non-additivity was found. An unfavorable exposure profile, primarily characterized by high Cu and low Zn levels, could lead to a significant increase in the risk of developing female breast cancer. Further studies are warranted to confirm these findings. Display omitted •Exposure to 16 metal(loid)s was assessed in 578 women from a multicenter cohort.•Breast cancer cases showed significantly higher Cu and lower Zn plasma levels.•The single-metal analysis found a positive association for Cu, Pb and W.•The mixture analysis identified Cu, Mn, Sb, V, W and Zn as the main components.•The joint effect of the metal mixture was a 4-fold increase in breast cancer risk.