Publication:

Factors affecting the assessment of mitotic count in histopathological sections of tumors: a study of interobserver and intraobserver variability

Background Mitotic count is the most commonly used method of assessing the proliferative activity of a tumor. It is usually done in routine Hematoxylin & Eosin stained sections and is used for classification, grading, prognostication of tumors and sometimes as a decision factor for treatment. There are numerous variables that can influence the mitotic count like delay in fixation, thickness of the section, size of the high power field of the microscopes and so on. This study is designed to assess the relative importance of Intra-observer variability and Inter-observer variability on mitotic counting by keeping all different procedural factors constant.

Methods Sections from forty cases of breast cancer and twenty cases of high grade lymphoma formed the study material. Mitotic counts done by the principal investigator under standard conditions were compared with counts done by another experienced observer under standard conditions to evaluate the inter-observer variability. The principal investigator will make all counts twice at intervals of one month to assess intra-observer variability. Paired t test and linear regression were the statistical tests used in analysis. Ki-67 immunohistochemistry was also done in sections fixed at different intervals.

Results Our study showed that inter-observer (p=0.261) and intra-observer variation (p=0.261) is not statistically significant. In case of inter-observer variability the correlation is weak and not significant.

Conclusions Reproducibility in mitotic counting can be achieved by following a strict morphological criteria as well as a strict counting protocol.