The effect of blood group phenotypes on the Ki-67 proliferation index in breast cancer

INTRODUCTION: The Ki-67 proliferation index is a key biomarker reflecting tumor aggressiveness and therapeutic response in breast cancer. The ABO blood group system, beyond its hematologic role, has been associated with cancer susceptibility, immune regulation, and inflammation. However, its potential influence on tumor proliferation remains unclear. This study aimed to evaluate the relationship between ABO/Rh blood groups and Ki-67 expression in breast cancer.
METHODS: A total of 189 patients diagnosed with breast malignancy between 2020 and 2024 were retrospectively analyzed. Clinical parameters including age, ABO and Rh blood groups, and Ki-67 index were recorded. Ki-67 expression was assessed immunohistochemically as the percentage of positively stained tumor nuclei. Intergroup differences were analyzed using the Kruskal–Wallis test for ABO groups and the Mann–Whitney U test for Rh factor. Statistical significance was set at p < 0.05.
RESULTS: The mean age was 57.7 ± 13.7 years, and the mean Ki-67 index was 25.9 ± 18.7% (median 22%). Mean Ki-67 values by blood group were: A = 27.7%, O = 19.7%, B = 31.9%, and AB = 31.2%. A borderline significant difference was observed, particularly between group O and groups B/AB (p = 0.06). No significant association was found with Rh factor (p > 0.05).
DISCUSSION AND CONCLUSION: ABO blood group phenotypes may affect proliferative behavior in breast cancer. Lower Ki-67 levels in group O and higher indices in groups B and AB suggest that genetically determined antigenic variations could modulate tumor biology through immune or adhesion-related pathways. Larger multicenter studies are warranted to validate these findings.