在美国，大约 20% 的乳腺癌表达 HER2 阳性受体。 HER2 受体免疫组织化学 (IHC) 染色结果模棱两可 (2 ) 通常需要进行荧光原位杂交 (FISH) 进行进一步分类。当前指南不建议对 IHC 阴性（0 或 1）病例进行常规 FISH 检测。本研究调查了一家对所有病例同时进行 IHC 和 FISH 检测的机构，以确定真正的 HER2 阳性率。对当时同时进行 HER2 IHC 和 FISH 检测的机构进行了 2015 年至 2021 年的回顾性图表审查。所有浸润性乳腺癌的诊断。确定真正的HER2阳性患者的比率，并进一步探讨患者和肿瘤特征。该机构总共收治了1835例浸润性乳腺癌病例。 IHC 和 FISH 检测中共有 289 例 HER2 阳性（15.7%）。另外 38 例在 IHC 中被确定为 HER2 阴性，但在反射 FISH 测试中被重新分类为 HER2 阳性。通过反射性 FISH 检测，HER2 阳性病例总数从 289 例 (15.7%) 增加到 327 例 (17.8%)。对 IHC 阴性肿瘤完成 FISH 检测后出现的额外 HER2 阳性病例表明，常规 FISH 检测可能还有作用标准 IHC 染色以确定乳腺癌的 HER2 状态。正确诊断的伦理、预后甚至益处超过了 FISH 测试的额外费用。© 2023。这是美国政府的作品，在美国不受版权保护；外国版权保护可能适用。

Approximately 20% of breast cancers express HER2-positive receptors in the USA. HER2 receptor immunohistochemistry (IHC) staining with equivocal (2+) results commonly undergoes fluorescence in-situ hybridization (FISH) for further classification. Current guidelines do not recommend routine FISH testing in IHC-negative (0 or 1+) cases. This study investigates an institution that performs both IHC and FISH testing on all cases to identify the true HER2-positive rate.A retrospective chart review from 2015 to 2021 was conducted at an institution where both HER2 IHC and FISH testing were performed at the time of diagnosis for all invasive breast cancers. The rate of true HER2-positive patients was determined, and patient and tumor characteristics were further explored.A total of 1835 invasive breast cancer cases were primarily treated at this institution. A total of 289 cases were HER2 positive on IHC and FISH testing (15.7%). An additional 38 cases were identified as HER2 negative on IHC, but reclassified as HER2 positive on reflex FISH testing. Total HER2 positive cases increased from 289 (15.7%) to 327 cases (17.8%) with reflex FISH testing.The additional HER2-positive cases after completing FISH testing on IHC-negative tumors suggests there may be a role for routine FISH testing in addition to standard IHC staining to determine HER2 status for breast cancer. The ethical, prognostic and even  benefits of a correct diagnosis outweigh the added expense of FISH testing.© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.