Background/Objectives: Zinc deficiency has been associated with increased cancer-related mortality, yet its prognostic relevance in patients with breast cancer and comorbid diabetes remains unclear. This study evaluated the association between zinc deficiency and adverse 5-year clinical outcomes in this population. Methods: This retrospective cohort study used the TriNetX database to identify women aged ≥20 years with breast cancer and type 2 diabetes who had recorded serum zinc levels within 3 months before the index date during the period from 1 January 2013 to 4 April 2026. Patients were categorized into zinc-deficiency, normal-zinc, or high-zinc groups. Outcomes included all-cause mortality, hospitalization, intensive care unit admission, and emergency department visits at the 1-, 3-, and 5-year follow-ups. Cox proportional hazards regression models were applied after 1:1 propensity score matching across 12 demographic and clinical variables. Results: Among 648 eligible patients, 282 had zinc deficiency, 311 had normal zinc levels, and 55 had high zinc levels. After matching, 218 remained in each of the zinc-deficient and control groups. Zinc deficiency was associated with higher all-cause mortality at 1 year (hazard ratio HR, 2.45; 95% CI, 1.41, 4.28), 3 years (hazard ratio HR, 2.09; 95% CI, 1.34, 3.28), and 5 years (HR, 1.92; 95% CI, 1.27, 2.92), as well as increased risks of emergency department visits, hospitalization, and ICU admission across follow-up periods. No significant differences were observed between the high-zinc and zinc-normal groups, possibly due to limited sample size. Subgroup analyses identified several exploratory subgroup-specific associations. Conclusions: Zinc deficiency was associated with poorer clinical outcomes in women with breast cancer and type 2 diabetes. However, because low serum zinc may also reflect malnutrition, systemic inflammation, frailty, or disease burden, these findings should be interpreted as hypothesis-generating rather than causal.
Chiang et al. (Thu,) studied this question.