Objective: To evaluate the use of stereologically estimated tumor cell counts in the mitotic index as well as to investigate its correlation with the currently used method and test the reproducibility of the method.
Study design: The stereologic method described by Simpson et al was used to estimate tumor cellularity in 50 invasive ductal carcinomas. Mitotic counts were also performed, and the mitotic index was calculated by the use of estimated tumor cell counts. Estimated cell counts and the mitotic index calculated were compared statistically with the actual cell counts and the traditional mitotic grades, respectively. Interobserver reproducibility of the method was also tested.
Results: Stereologically estimated tumor cell counts had a good correlation with actual cell counts (r = .891, P < .001). Besides, the mitotic indices calculated with tumor cell counts (calculated with both estimated and actual cell counts) in the denominator of the fraction of the mitotic index were in agreement with the currently used method (P < .01 for both). There was no statistically significant difference between the counts of two observers (P = .068).
Conclusion: The suggested method, considering tumor cellularity as an influencing factor, was practical, reproducible and in agreement with the traditional method. This method should be studied in a large group of patients with follow-up data to determine the threshold values for different grades and determine its prognostic value during the disease course.