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Context.— Breast carcinoma grade, as determined by the Nottingham Grading System (NGS), is an important criterion for determining prognosis. The NGS is based on 3 parameters: tubule formation (TF), nuclear pleomorphism (NP), and mitotic count (MC). The advent of digital pathology and artificial intelligence (AI) have increased interest in virtual microscopy using digital whole slide imaging (WSI) more broadly. Objective.— To compare concordance in breast carcinoma grading between AI and a multi-institutional group of breast pathologists using digital WSI. Design.— We have developed an automated NGS framework using deep learning. Six pathologists and AI independently reviewed a digitally scanned slide from 137 invasive carcinomas and assigned a grade based on scoring of the TF, NP, and MC. Results.— Interobserver agreement for the pathologists and AI for overall grade was moderate (κ = 0.471). Agreement was good (κ = 0.681), moderate (κ = 0.442), and fair (κ = 0.368) for grades 1, 3, and 2, respectively. Observer pair concordance for AI and individual pathologists ranged from fair to good (κ = 0.313–0.606). Perfect agreement was observed in 25 cases (27.4%). Interobserver agreement for the individual components was best for TF (κ = 0.471 each) followed by NP (κ = 0.342) and was worst for MC (κ = 0.233). There were no observed differences in concordance amongst pathologists alone versus pathologists + AI. Conclusions.— Ours is the first study comparing concordance in breast carcinoma grading between a multi-institutional group of pathologists using virtual microscopy to a newly developed WSI AI methodology. Using explainable methods, AI demonstrated similar concordance to pathologists alone.

Context.— The Ventana programmed death ligand-1 (PD-L1) SP142 immunohistochemical assay (IHC) is approved by the US Food and Drug Administration as the companion diagnostic assay to identify patients with locally advanced or metastatic triple-negative breast cancer for immunotherapy with atezolizumab, a monoclonal antibody targeting PD-L1. Objective.— To determine interobserver variability in PD-L1 SP142 IHC interpretation in invasive breast carcinoma. Design.— The pathology database was interrogated for all patients diagnosed with primary invasive, locally recurrent, or metastatic breast carcinoma on which PD-L1 SP142 IHC was performed from November 2018 to June 2019 at our institution. A subset of cases was selected using a computerized random-number generator. PD-L1 IHC was evaluated in stromal tumor-infiltrating immune cells using the IMpassion130 trial criteria, with positive cases defined as immunoreactivity in immune cells in 1% or more of the tumor area. IHC was interpreted on whole slide images by staff pathologists with breast pathology expertise. Interobserver variability was calculated using unweighted κ. Results.— A total of 79 cases were assessed by 8 pathologists. Interobserver agreement was substantial (κ = 0.727). There was complete agreement among all 8 pathologists in 62% (49 of 79) of cases, 7 pathologists or more in 84% (66 of 79) of cases, and 6 pathologists or more in 92% (73 of 79) of cases. In 4% (3 of 79) of cases, all of which were small biopsies, pathologists' interpretations were evenly split between scores of positive and negative. Conclusions.— The findings show substantial agreement in PD-L1 SP142 IHC assessment of breast carcinoma cases among 8 pathologists at a single institution. Further study is warranted to define the basis for discrepant results.

ContextRadial scars are benign sclerosing lesions that are routinely excised when diagnosed in a needle core biopsy. Optimal management for patients with incidental and small (≤5 mm) radial scars is uncertain.ObjectiveTo assess pathologic upgrade of radial scars diagnosed in needle core biopsy samples and identify a subset of patients who could benefit from conservative management.DesignPatients with a diagnosis of radial scar in a needle core biopsy who underwent excision of the biopsied area were identified. Radial scars greater than 5 mm in size and those with coexisting atypia, carcinoma, and papillary lesions were excluded. After histologic-radiographic correlation, rates of pathologic upgrade were assessed.ResultsSeventy-seven radial scars diagnosed in 66 patients were included. Overall, 9 of 77 (12%) showed upgrade to a high-risk lesion (6 lobular carcinoma in situ, 2 atypical ductal hyperplasia, 1 atypical lobular hyperplasia), while none (0%) showed upgrade to invasive carcinoma or ductal carcinoma in situ. One of 22 incidental radial scars (4.5%) showed upgrade on excision versus 6 of 36 (16.7%) for radial scars considered to be the radiographic target (P = .23). Older age was associated with upgrade (P < .001).ConclusionsNo incidental or small (≤5 mm) radial scars excised revealed invasive carcinoma or ductal carcinoma in situ on excision. Provided there is good pathologic-radiologic concordance, it appears reasonable for these patients to be managed conservatively.