Does Nottingham grading of primary invasive breast carcinomas in an Adelaide metropolitan hospital pathology department adhere to the recommended distribution of grading?

Background and purpose: The Nottingham grading system for primary invasive breast carcinomas (PIBC) was developed to improve histologic grading by adding quantitative cut-offs, however, reproducibility and consistency have remained concerns. The recommended grading distribution is approximately 20% cases grade 1, 40% grade 2 and 40% grade 31-2. The purpose of this audit was to determine whether distribution of grade for PIBC at Flinders Medical Centre (FMC) falls within the recommended spectrum. Methods: All graded PIBC on core biopsy, partial or total mastectomy between 01 January and 31 December 2021 at FMC reported by a pathologist assessing a minimum of 20 PIBC were included (277 cases, 4 pathologists). Proportion of cases assigned to each grade was compared with the standard1-2. Screening status was recorded to compare grading of screened with unscreened population. HER-2 and lymphovascular invasion (LVI) (partial/total mastectomy cases only) were compared with values in the literature. Results: The overall distribution for the 277 cases was 25% (69) grade 1, 49% (135) grade 2 and 26% (73) grade 3; 3 out of 4 pathologists assigned over 50% of their cases a grade of 2. There were 64(23%) screen-detected and 213(77%) non-screen detected cases. PIBC was grade 1 in 40.6% (26) screened and 20.2% (43) unscreened, grade 2 in 39.1% (25) screened and 51.7% (110) unscreened, and grade 3 in 20.3% (13) screened and 28.2% (60) unscreened cases. HER-2 was positive in 32(12%) and negative in 245(88%). LVI was present in 26% (44) cases, suspicious in 2% (4) and absent in 72% (121). Conclusions: Overall grading between most pathologists was similar with a somewhat higher level of grade 2 cases compared with the standard. A likely reason is that 23% of cases were screen-detected with expected lower grade cancers, which may additionally explain the slightly lower proportion of HER-2 amplified cases. The proportion of cases with LVI was consistent with the literature. References: 1. Elston CW (1984). The assessment of histological differentiation in breast cancer. Aust N Z J Surg 54:11, 15. 2. Rakha EA, El-Sayed ME, Lee AH et al (2008). Prognostic significance of Nottingham histologic grade in invasive breast carcinoma. J Clin Oncol 26(19):3153–3158.