USE OF THE MITOTIC COUNTS FOR THE PROGNOSIS AND GRADING OF BREAST-CANCER - METHOD EVALUATION STUDY

Reproducibility of the volume fraction-corrected mitotic index (M/V(V) index) was studied in 144 unselected breast cancer specimens. The inf luence on decision making of variation in determining the index was al so analysed. - In the complete series of specimens the correlation bet ween two observers, one subjectively estimating the epithelial fractio n of tumor epithelium and the other using point-counting (10 x 10 ocul ar grid), was good (Pearson's r = 0.82, p < 0.001, 95% CI 0.70-0.92). - A subset of 30 specimens was used to evaluate the grading efficiency (GE) of the M/V(V) index method. The mean grading efficiency as estim ated from this subset varied between 90% and 93%. The average minimum GE value was 82.8% (SD = 3.4%). The findings suggest that when the M/V (V) index method is used, the grading is correct on average in 90% or more of the cases, but dependant on the cutoff point. The over-all gra ding efficiency of the M/V(V) index method was at least 85% at all cut points in both series. The GE-value of the M/V(V) index method was com parable to that obtained from published S-phase fraction data on breas t cancer specimens from three independed laboratories. We conclude tha t the M/V(V) index in breast cancer analysis is a sufficiently reprodu cible method in mitosis counting, and that it can be used with subject ive or point count estimation of the area fraction of neoplastic epith elium.