An International Ki67 Reproducibility Study in Adrenal Cortical Carcinoma

Abstract

Despite the established role of Ki67 labeling index in prognostic stratification of adrenocortical carcinomas and its recent integration into treatment flow charts, the reproducibility of the assessment method has not been determined. The aim of this study was to investigate interobserver variability among endocrine pathologists using a web-based virtual microscopy approach. Ki67-stained slides of 76 adrenocortical carcinomas were analyzed independently by 14 observers, each according to their method of preference including eyeballing, formal manual counting, and digital image analysis. The interobserver variation was statistically significant (P<0.001) in the absence of any correlation between the various methods. Subsequently, 61 static images were distributed among 15 observers who were instructed to follow a category-based scoring approach. Low levels of interobserver (F=6.99; Fcrit=1.70; P<0.001) as well as intraobserver concordance (n=11; Cohen κ ranging from -0.057 to 0.361) were detected. To improve harmonization of Ki67 analysis, we tested the utility of an open-source Galaxy virtual machine application, namely Automated Selection of Hotspots, in 61 virtual slides. The software-provided Ki67 values were validated by digital image analysis in identical images, displaying a strong correlation of 0.96 (P<0.0001) and dividing the cases into 3 classes (cutoffs of 0%-15%-30% and/or 0%-10%-20%) with significantly different overall survivals (P<0.05). We conclude that current practices in Ki67 scoring assessment vary greatly, and interobserver variation sets particular limitations to its clinical utility, especially around clinically relevant cutoff values. Novel digital microscopy-enabled methods could provide critical aid in reducing variation, increasing reproducibility, and improving reliability in the clinical setting.

The Utrecht Score: A novel histopathological scoring system to assess the prognosis of dogs with cortisol‐secreting adrenocortical tumours

“…To standardize Ki67 PI scoring as much as possible, we suggest to analyse the Ki67 PI in hot spot areas, to capture images of these areas, to count at least 1000 nuclei, and to use ImageJ or similar software to keep track of the number of counted positive and negative cells. A drawback of this method is that it is time‐consuming, but developments in digital microscopy‐enabled methods could facilitate future reproducible and reliable Ki67 PI assessments …”

“…A recent study on human ACCs reported low intra-and interobserver agreement scores for Ki67 scoring among 14 trained endocrine pathologists. 23 However, in that study each observer was allowed to perform the analyses according to their own method of preference, which included visual estimation, formal manual count, and digital image analysis. In our study, the inter-observer agreement of the Ki67 PI was excellent, which is most likely associated with the methodology used.…”

MANAGEMENT OF ENDOCRINE DISEASE: Adrenocortical carcinoma: differentiating the good from the poor prognosis tumors

“…A recent study has evaluated the inter-observer variability of Ki67 scoring assessment in ACC among 14 trained endocrine pathologists. Low levels of interobserver and intra-observer concordance were observed (54), especially for intermediate Ki67 indexes (10-30%). This may be a concern for clinical practice since the clinically relevant cutoff values are in this range.…”

The next step: mechanisms driving adrenocortical carcinoma metastasis

“…Furthermore, Ki67 LI integration with morphological parameters in the newly introduced Helsinki score makes it to outperform the Weiss system as a prognostic indicator in ACC (see above) (Pennanen et al 2015, Duregon et al 2017. However, a limitation of the Ki67 LI consists in difficulties in its standardization and reproducibility when applied to many tumor types, including ACC (Papathomas et al 2016). These data indicate that other markers are needed to complement the Ki67 LI in the assessment of malignancy in ACC.…”