浸润性小叶癌（ILC）具有独特的形态学和与E-cadherin功能丧失的关联。它具有特殊的临床和影像特征，正确识别它很重要。根据最近的建议，我们测试了E-cadherin免疫组织化学（IHC）在识别ILC中的常规应用的价值。从四个匈牙利机构中的五名乳腺病理经验丰富的病理学家对1001例乳腺癌进行了组织类型学分类，这些癌症来自诊断性活检或切除标本，随机分配为首先进行苏木精-伊红（HE）诊断，然后进行E-cadherin IHC；或直接进行HE和基于E-cadherin的诊断。在524例HE诊断中，有73例（14%）被认为是不确定的。E-cadherin在14例（2.7%）病例中进行了初始组织学类型修改，其中包括3例在HE基础上明确的类型分配。在立即进行双重评估的477例（18%）中，认为使用E-cadherin免疫染色有用，并且类型的不确定性降至5%（25例），但不为零。对171例不确定、困难、非典型病例进行集体评估，大多数病例达成了共识诊断，但有15例对于其适当的组织学类型仍存在疑虑。对13例进行了CDH1基因测序尝试，并成功获得7例病例的致病性遗传变异。E-cadherin IHC的常规使用降低了类型学中的不确定性，并提高了类型学的准确性，但可能会增加不必要的额外免疫染色成本。此外，这一程序不能排除由于E-cadherin阳性的ILC而产生的不确定性，尤其是当生长模式不典型时。© 2023 John Wiley＆Sons Ltd.

Invasive lobular carcinoma (ILC) has distinct morphology and association with loss of E-cadherin function. It has special clinical and imaging features, and its proper recognition is important. Following a recent proposal, we tested the value of the routine use of E-cadherin immunohistochemistry (IHC) in recognizing ILC.Five pathologists with experience in breast pathology from four Hungarian institutions histotyped 1001 breast cancers from diagnostic core biopsies or excision specimens randomly assigned to haematoxylin and eosin (HE) diagnosis first, followed by E-cadherin IHC; or to immediate HE and E-cadherin-based diagnosis. Of 524 cases with HE diagnosis, 73(14%) were deemed uncertain. E-cadherin made the initial histological type change in 14/524 cases (2.7%), including three with confident HE-based type allocation. Use of E-cadherin immunostaining was considered useful in 88/477 cases (18%) with immediate dual assessment, and typing uncertainty went down to 5% (25/477 cases), but was not zero. Collective assessment of 171 uncertain, difficult, nonclassical cases resulted in consensus diagnosis in most cases, but 15 cases were still doubtful as concerns their proper histological type. CDH1 gene sequencing was attempted and successful in 13; pathogenic genetic alterations were identified in seven cases.The routine use of E-cadherin IHC decreases the uncertainty in typing and improves the typing accuracy at the cost of potentially redundant additional immunostains. Furthermore, this procedure does not exclude uncertainty due to E-cadherin-positive ILCs, which are occasionally difficult to confidently label as ILC, especially when the growth pattern is not classic.© 2023 John Wiley & Sons Ltd.