AGE AND SITE-SPECIFIC VARIATIONS IN KI-67 EXPRESSION IN PERIPHERAL ZONE LESIONS OF THE PROSTATE: A PROSPECTIVE OBSERVATIONAL STUDY

Background: Prostatic adenocarcinoma predominantly originates within the peripheral zone (PZ), and its biologicalbehaviour is influenced by patient age as well as the anatomical location of the tumour within the gland. Ki-67, a nuclearproliferation-associated antigen detectable only in actively cycling cells, enables quantification of tumour cell proliferativeactivity by immunohistochemistry.[2,3,7] Prospective evidence delineating how Ki-67 expression is modulated by age andbiopsy subsite within the prostatic PZ remains limited. The objective is to evaluate age- and site-specific differences in Ki-67labeling index (LI) in peripheral zone lesions of the prostate, to correlate Ki-67 with clinicopathological parameters (PSA,Gleason score, tumour stage), and to identify anatomical hotspots of elevated proliferative activity. Materials and Methods:A prospective observational study was conducted from August 2022 to August 2025 in the Department of Pathology at atertiary care hospital. Sixty patients who underwent transrectal ultrasound (TRUS)-guided site-mapped biopsies from six PZsubsites (right/left base, mid, apex) were enrolled. Ki-67 LI was calculated as the percentage of positively stained nucleiamong ≥500 lesional cells per core. Statistical associations were evaluated using one-way ANOVA with post-hoc Tukey testand the Kruskal–Wallis test, with p<0.05 considered significant. Results: Of 60 cases, 46 (76.6%) were adenocarcinomas, 6(10%) were high-grade prostatic intraepithelial neoplasia (HGPIN), and 8 (13.3%) were benign. Mean Ki-67 LI increasedprogressively with age (6.2% in the 40–49 age group to 21.4% in those ≥80 years). Among the six biopsy subsites, the rightapex showed the highest mean Ki-67 LI (20.5%), while the right base showed the lowest (10.7%). Ki-67 LI correlatedsignificantly with PSA levels (p = 0.04), Gleason score (p = 0.02), and tumour stage (p = 0.03). Conclusion: Ki-67expression in PZ lesions rises steadily with patient age and is highest at apical biopsy sites, suggesting these areas havegreater tumour cell growth activity. Routine use of Ki-67 immunostaining in pathology reports and ensuring adequate apicalsampling during TRUS-guided biopsy may improve both diagnostic accuracy and prognostic grading.