ERBB2 and cancer: In HR+/HER2+ (n=4) and HR+/HER2− (n=5) subtypes, most non-responders showed near-zero or negative ΔCopper, whereas in TNBC, the single non-responder, who subsequently relapsed, demonstrated consistently positive ΔCopper values at both follow-up timepoints, which were specifically measured to track changes post-treatment and at cancer relapse (Figure 5A).