ASSOCIATION OF KI-67 PROLIFERATION INDEX WITH NOTTINGHAM HISTOLOGICAL GRADE IN INVASIVE DUCTAL CARCINOMA OF THE BREAST: A RETROSPECTIVE OBSERVATIONAL STUDY

Background: Ki-67 is an immunohistochemical marker of cellular proliferation that has been extensively investigated inbreast carcinoma. Nottingham histological grade (NHG) is an established morphological grading system based on tubuleformation, nuclear pleomorphism, and mitotic activity and has recognized prognostic value in invasive breast carcinoma.[1]Although mitotic activity contributes to histological grading, Ki-67 and NHG assess different aspects of tumor biology. Thisstudy evaluated the association between Ki-67 proliferation index and Nottingham histological grade in invasive ductalcarcinoma of the breast. Materials and Methods: A retrospective observational analysis was performed using the breastcarcinoma master dataset. Cases with documented invasive ductal carcinoma, available Nottingham histological grade, andreported Ki-67 proliferation index were considered eligible. Ki-67 values reported as ranges were represented by theirmidpoint, whereas values reported with inequality signs were represented by the stated numerical boundary for exploratorystatistical analysis. Ki-67 distributions were compared across Nottingham grades using the Kruskal–Wallis test, and therelationship between grade and Ki-67 was additionally assessed using Spearman rank correlation. A two-sided p value <0.05was considered statistically significant. Results: Among 44 evaluable cases, 7 were Nottingham grade 1, 31 were grade 2, and6 were grade 3. Median Ki-67 proliferation indices were 10.0%, 12.5%, and 8.5% in grades 1, 2, and 3, respectively. MeanKi-67 values were 10.36%, 15.41%, and 11.62%, respectively. There was no statistically significant difference in Ki-67distribution across Nottingham grades (Kruskal–Wallis H=1.147, p=0.563). Spearman rank correlation likewise demonstratedno significant monotonic relationship between Nottingham grade and Ki-67 (ρ=0.046, p=0.765). Conclusion: In thisretrospective dataset, Ki-67 proliferation index was not significantly associated with Nottingham histological grade. Thefindings suggest that morphological grade and proliferative activity may provide complementary rather than interchangeableinformation in individual breast carcinomas. The absence of a significant association should be interpreted cautiously becauseof the limited sample size, unequal representation of grade groups, and variability in the manner in which Ki-67 was originallyreported. Larger studies using standardized Ki-67 assessment are warranted.