Janina Kulka

Aims 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. Methods and results 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. Conclusions 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.