Table_1_HER2-low metastases of HER2-negative primary tumors: a single institution analysis of intertumoral and internodal heterogeneity in node-positive breast cancer.docx

ObjectiveHER2 status in breast cancer is an essential parameter in individual therapeutic decision-making and is routinely assessed in primary tumors in accordance with international recommendations. Reports of HER2 heterogeneity raise the question of basing treatment decisions on HER2 status in metastases, if present. We investigated the degree and clinical implications of HER2 heterogeneity in lymph node–positive breast cancer. Because of recent recognition of therapeutic opportunities in this group of tumors, we especially focused on cases involving low-level HER2 expression.
MethodsThe HER2 status of primary tumors and of corresponding lymph node metastases was determined in archived material at the protein and gene levels using the gene– protein assay and interpreted in accordance with 2018 ASCO/CAP criteria. HER2-low status was defined as protein expression levels 1+ or 2+ with negative amplification status.
ResultsWe analyzed a series of 43 cases of primary infiltrating breast cancer, each with at least two axillary nodes harboring macrometastases (>2 mm), in total 206 such nodes. In 7% of cases, we detected intertumoral HER2 heterogeneity. Three of nine HER2-positive primary tumors were associated with HER2-negative metastases. No cases with HER2-negative primary tumors had HER2-positive metastases, but 55% (6/11) of HER2 0 primary tumors had HER2 1+ and/or 2+ metastases, and 19% (3/16) HER2 1+ cases had exclusively HER2 0 metastases. All metastases in HER2 2+ cases showed HER2-low protein expression levels. Internodal HER2 heterogeneity at low protein expression levels (presence of HER2 0, HER2 1+, and/or HER2 2+ metastatic deposits within the same axilla) was seen in 40% (17/43) of cases. We found no statistically significant association between HER2 heterogeneity and other tumor-related parameters. Survival data indicated worse outcomes in the HER2-low group compared with the rest of the cohort.
ConclusionOur results indicate a substantial instability of HER2 protein expression, leading to considerable intertumoral and internodal HER2 heterogeneity in lymph node–positive breast carcinomas. This heterogeneity is particularly relevant in HER2-low tumors in which the corrective effects of HER2 gene copy number analysis definitionally is absent. Our findings suggest that determining HER2 status in metastatic lymph nodes may generate relevant information for therapeutic decision-making.

目的：乳腺癌人表皮生长因子受体2（HER2）状态是个体化治疗决策的核心参数，依据国际指南，原发肿瘤的HER2状态检测已成为临床常规操作。有关HER2异质性的相关报道提出了一个关键问题：若存在转移灶，治疗决策是否应基于转移灶的HER2状态？本研究旨在探讨淋巴结阳性乳腺癌中HER2异质性的程度及其临床意义。鉴于近期学界对该类肿瘤治疗靶点的新认知，我们特别聚焦于低水平HER2表达的病例。方法：本研究采用基因-蛋白联合检测技术，对存档样本中的原发肿瘤及其对应淋巴结转移灶的HER2状态分别进行蛋白水平与基因水平检测，并依据2018年美国临床肿瘤学会/美国病理学家协会（ASCO/CAP）指南进行结果判读。本研究将HER2低表达定义为蛋白表达水平为1+或2+且基因扩增状态为阴性。结果：本研究共纳入43例原发性浸润性乳腺癌病例，所有病例均至少存在2枚伴大体转移（直径＞2mm）的腋窝淋巴结，累计纳入转移淋巴结206枚。在7%的病例中检测到瘤间HER2异质性。9例HER2阳性原发肿瘤中，有3例对应的转移灶呈HER2阴性。未观察到原发肿瘤为HER2阴性而转移灶为HER2阳性的病例；但在11例HER2 0型原发肿瘤中，55%（6/11）的病例其转移灶呈HER2 1+和/或2+表达；16例HER2 1+型原发肿瘤中，19%（3/16）的病例其转移灶仅呈HER2 0表达。所有HER2 2+型原发肿瘤对应的转移灶均表现为HER2低水平蛋白表达。在40%（17/43）的病例中观察到结间HER2异质性，即同一腋窝内存在不同HER2蛋白表达水平的转移灶（包含HER2 0、HER2 1+和/或HER2 2+转移灶）。本研究未发现HER2异质性与其他肿瘤相关参数存在统计学显著关联。生存分析结果显示，HER2低表达组的预后较队列其余患者更差。结论：本研究结果表明，HER2蛋白表达存在显著不稳定性，可导致淋巴结阳性乳腺癌出现明显的瘤间及结间HER2异质性。这种异质性在HER2低表达肿瘤中尤为关键，因为此类肿瘤本就不存在HER2基因拷贝数分析的校正效应。本研究结果提示，对转移淋巴结的HER2状态进行检测，可为临床治疗决策提供有价值的参考信息。