Grading of breast cancer on needle core biopsy: does a reduction in mitotic count threshold improve agreement with grade on excised specimens?

Background: Accurate assessment of invasive breast cancer grade on needle core biopsy (NCB) is important as it guides treatment.

Aim: To assess the agreement between grade of invasive cancer on NCB and excision and determine whether altering the mitotic count score threshold on NCB improves it.

Methods: Pathology slides from patients with an NCB diagnosis of invasive breast cancer who underwent subsequent breast conservation surgery in 2012 were reviewed. Mitotic counts were assessed and tumour grade agreement between NCB and excision evaluated. The mitotic count thresholds were altered and grade agreement was reassessed.

Results: In 283/359 (79%) cases, there was concurrence on histological grade between NCB and excision. Reduction in mitotic count thresholds did not improve either overall tumour grade agreement or agreement within any subgroup of patients.

Conclusions: In our experience, the current mitotic count score thresholds are appropriate and should be maintained.