Comparison between whole mount tissue preparations and virtual tissue microarray samples for measuring Ki-67 and apoptosis indices in human bladder cancer: A cross-sectional study

Recent tissue microarray (TMA)-based studies have shown that cell proliferation- and apoptosis-related biomarkers are associated with clinical outcomes in patients with bladder urothelial carcinoma. However, little is known about the differences in these biomarker measurements between whole mount tissue preparations and TMAs. This study aimed to elucidate the discrepancy in the measurements of Ki-67 indices (KIs) and apoptosis indices (AIs) between whole mount tissue preparations and TMAs of bladder urothelial carcinoma samples. Whole mount tissue preparations for Ki-67 immunohistochemistry and terminal deoxynucleotidyl transferase dUTP nick end labeling were made from 30 patients who underwent transurethral resection of bladder urothelial carcinoma. Digital microscopy-assisted virtual TMAs, consisting of 3 small round areas (1 or 0.6 mm in diameter), were generated from the same whole mount tissue preparations. The measurement results in highly reactive areas of biomarkers were compared between the whole mount tissue preparation- and the TMA-based methods. Bland-Altman plot analysis, regression analysis, and Kendall τ were performed to investigate differences in the measurement results, systematic biases, and correlations between biomarkers. Although the Bland-Altman plot analysis demonstrated that almost all the plots were within the limits of agreement, fixed biases were detected in the 1- and 0.6-mm TMAs for the KI (0.181 and 0.222, respectively) and the AI (0.055 and 0.063, respectively). Proportional biases were also detected in the 1- and 0.6-mm TMAs for the AI (P < 0.001 and P < 0.001, respectively). Furthermore, positive correlations between KIs and AIs were observed in whole mount tissue preparations (r = 0.260, P = 0.044) and in the 1 mm TMAs (r = 0.375, P = 0.004); however, no such correlation was observed in the 0.6 mm TMAs. Our study suggests that the measurement results for certain biomarkers of bladder urothelial carcinoma obtained from TMA-based samples can be susceptible to systematic bias, and the lack of correlation between biomarkers cannot be avoided as it is in whole mount tissue preparations. Virtual TMAs can help identify systematic bias and establish a better sampling strategy prior to performing high-throughput TMAs for biomarker studies.