Aims Histological grade is widely used to guide the management of invasive breast cancer (IBC). Yet, substantial interlaboratory and intralaboratory grading variations exist in daily pathology practice. To create awareness and to facilitate quality improvement, feedback reports, containing case-mix-adjusted laboratory-specific grades benchmarked against other laboratories, were sent to the individual laboratories by 1 March 2018. We studied the effect of these feedback reports on interlaboratory grading variation up till 1 year later.

Methods Overall, 17 102 synoptic pathology reports of IBC resection specimens from 33 laboratories, obtained between 1 March 2017 and 1 March 2019 were retrieved from the Dutch Pathology Registry (PALGA). An overall deviation score (ODS), representing the sum of deviations from the grade-specific overall proportions, was calculated to compare the absolute deviation for all grades at once. Case-mix correction was performed by two multivariable logistic regression analyses, providing laboratory-specific ORs for high-grade versus low-grade IBC.

Results After feedback, the overall range between laboratories decreased by 3.8%, 6.4% and 6.6% for grades I, II and III, respectively. Though the mean ODS remained similar (13.8% vs 13.7%), the maximum ODS decreased from 34.1% to 29.4%. The range of laboratory-specific ORs decreased by 21.9% for grade III versus grades I–II.

Conclusions An encouraging decrease in grading variation of IBC was observed after laboratory-specific feedback. Nevertheless, the overall grading variation remains substantial. In view of the important role of grading in patient management, it is adamant that not only feedback should be provided on a regular basis but also other interventions, such as additional training, are required.