Aims: Histological grade assessed on core biopsy of mammary invasive carcinomas tends to underestimate the grade in the excision specimen. A major factor is underestimation of mitoses. The aim of this study was to improve the assessment of mitoses in core biopsies.
Methods and results: In a test set (100 tumours), reducing the threshold for a mitotic score of 2 from 11 mitoses per 10 high-power fields (diameter 0.61 mm) to 6/10 resulted in improved agreement between core and excision from 69% to 73%. In tumours graded as T3 P3 M1 (few tubules, marked nuclear pleomorphism and few mitoses) on core (a group with poor agreement of grade between core and surgical specimens), this change in threshold also improved agreement in four tumours. Use of the mitotic count in the core of axillary nodal metastasis, if higher than the count in the breast core, improved agreement in two patients. Use of both approaches in a validation set (349 tumours) improved agreement from 65% to 70% in the whole group, and from 31% to 55% in tumours scored as T3 P3 M1 on the core.
Conclusions: These strategies improve the accuracy of grading on core biopsy and are of particular value in T3 P3 M1 tumours.
© 2011 Blackwell Publishing Limited.