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.
