LUMINA试验证明，在低危Luminal A乳腺癌（定义为I-II级，T1N0，激素受体阳性，HER2阴性和Ki67指数≤13.25％）中，年龄≥55岁的女性进行了保乳手术和内分泌治疗（但没有其他全身治疗），显示了非常低的局部复发率，支持在这些女性中安全省略放疗。在这里，我们描述了Ki67评估的方案，这是用于指导辅助放射治疗省略的伴随诊断测试。 Ki67免疫组化测试在三个区域实验室之一的全面切片上进行。受过国际Ki67乳腺癌工作组（IKWG）方法培训的病理学家，在扫描的标本玻片上标定肿瘤区域，并从至少五个随机选择的1毫米视野中评分100个细胞核。对于具有高Ki67异质性的病例，选择并评分进一步的虚拟核心，以确信将病例确定为Luminal A（≤13.25％）或B（> 13.25个％）。通过研究期间的年度质量保证计划评估了实验室间的变异性。 从质量保证计划中，所有病例/实验室的平均Ki67指数为13％。观察到的组内相关系数（ICC）和kappa统计量均≥0.9和≥0.7，表明有相当程度的一致性。中位评分时间为每例4分钟。从玻片直接进行的IKWG推荐的评分方法，需要评分最多四个视野，与LUMINA评分方法一致（ICC≥0.9）。 Ki67是一项实用，可重复性和廉价的生物标志物，可以识别低危Luminal A乳腺癌，作为放疗减弱的潜在候选者。 ClinicalTrials.gov编号，NCT01791829.©2023 The Authors. Histopathology由John Wiley & Sons Ltd.发表。

The LUMINA trial demonstrated a very low local recurrence rate in women ≥55 years with low-risk luminal A breast cancer (defined as grade I-II, T1N0, hormone receptor positive, HER2 negative and Ki67 index ≤13.25%) treated with breast-conserving surgery and endocrine therapy (but no other systemic therapy), supporting the safe omission of radiation in these women. Here we describe the protocol for Ki67 assessment, the companion diagnostic used to guide omission of adjuvant radiotherapy.Ki67 immunohistochemistry was performed on full-face sections at one of three regional labs. Pathologists trained in the International Ki67 in Breast Cancer Working Group (IKWG) method demarcated tumour areas on scanned slides and scored 100 nuclei from each of at least five randomly selected 1-mm fields. For cases with high Ki67 heterogeneity, further virtual cores were selected and scored in order to confidently assign a case as luminal A (≤13.25%) or B (>13.25%). Interlaboratory variability was assessed through an annual quality assurance programme during the study period.From the quality assurance programme, the mean Ki67 index across all cases/labs was 13%. The observed intraclass correlation coefficient (ICC) and kappa statistics were ≥0.9 and ≥0.7, respectively, indicating a substantial level of agreement. Median scoring time was 4 min per case. The IKWG-recommended scoring method, performed directly from slides, requiring up to four scored fields, is concordant with the LUMINA scoring method (ICC ≥ 0.9).Ki67 is a practical, reproducible, and inexpensive biomarker that can identify low-risk luminal A breast cancers as potential candidates for radiation de-escalation.ClinicalTrials.gov number, NCT01791829.© 2023 The Authors. Histopathology published by John Wiley & Sons Ltd.