Nottingham-defined mitotic score: comparison with visual and image cytometric phosphohistone H3 labeling indices and correlation with Oncotype DX recurrence score.

Prognosis of breast cancer patients has been determined traditionally by lymph node status, tumor size, and histologic grade. In recent years the Oncotype DX recurrence score (RS) assay has emerged as an expensive adjunct prognostic tool. Markers of proliferation play a large role in determination of RS, and we have shown previously that immunohistochemical expression of proliferation markers Ki-67 and phosphohistone H3 (PPH3) correlates with RS. Our current goal is comparison of the hematoxylin and eosin (H&E) mitotic score, defined by the Nottingham grading system, with anti-PPH3 mitotic figure labeling assessed by both visual and automated image analysis and correlation of mitotic score results with RS. Estrogen receptor-positive breast carcinomas from 137 patients with Oncotype DX testing were selected. A representative H&E-stained tumor section was evaluated. Mitoses were counted per 10 high-power fields and tumors graded using the Nottingham criteria by 1 pathologist in accordance with College of American Pathologists-recommended mitotic count cutoffs for a field diameter of 0.55 mm. An additional section was immunostained with PPH3 antibody. PPH3 mitotic scores were determined visually and by automated imaging system. Statistical analysis was performed using univariate tests and Spearman coefficient. There was a statistically significant positive correlation among the 3 methods of mitotic score assessment. Specifically, correlation of tumor grades obtained using visual and automated methods of assessment of mitotic activity with PPH3 stain was the strongest and most statistically significant (weighted κ value 0.84, P<0.001; Spearman coefficient 0.89, P<0.001). There was a statistically significant positive correlation between H&E mitosis score and RS (P<0.001, Spearman coefficient 0.30) and between visual PPH3 mitotic score and RS (P<0.001, Spearman coefficient 0.28). In conclusion, mitotic score by any of the 3 methods studied may be useful in assessing tumor grade, proliferation, and prognosis.