Quantification of tumor cellularity and mitotic index in invasive ductal carcinoma of the breast

OBJECTIVE: To evaluate the use of stereologically estimated tumor cell coun ts 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 decribed by Simpson et al teas used to estimate tumor cellularity in 50 invasive ductal carcinomas. Mitotic count s were also performed, and the mitotic index was calculated by the use of e stimated tumor cell counts. Estimated cell counts and the mitotic index cal culated were compared statistically with the actual cell counts and the tra ditional 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 actu al cell counts) in the denominator of the fraction of the mitotic index wer e in agreement with the currently used method (P < .01 for both). There was no statistically significant difference between the counts of two observer s (P = .068). CONCLUSION: The suggested method, considering tumor cellularity as an influ encing factor, teas practical, reproducible and in agreement with the tradi tional method. This method should be studied in a large group of patients w ith follow-up data to determine the threshold values for different grades a nd determine ifs prognostic value during the disease course.