Invasive lobular carcinoma (ILC) represents the second most common subtype of breast
cancer (BC), accounting for up to 15% of all invasive BC. Loss of cell adhesion due
to functional inactivation of E-cadherin is the hallmark of ILC. Although the current
world health organization (WHO) classification for diagnosing ILC requires the recognition
of the dispersed or linear non-cohesive growth pattern, it is not mandatory to demonstrate
E-cadherin loss by immunohistochemistry (IHC). Recent results of central pathology
review of two large randomized clinical trials have demonstrated relative overdiagnosis
of ILC, as only similar to 60% of the locally diagnosed ILCs were confirmed by central
pathology. To understand the possible underlying reasons of this discrepancy, we undertook
a worldwide survey on the current practice of diagnosing BC as ILC. A survey was drafted
by a panel of pathologists and researchers from the European lobular breast cancer
consortium (ELBCC) using the online tool SurveyMonkey (R). Various parameters such
as indications for IHC staining, IHC clones, and IHC staining procedures were questioned.
Finally, systematic reporting of non-classical ILC variants were also interrogated.
This survey was sent out to pathologists worldwide and circulated from December 14,
2020 until July, 1 2021. The results demonstrate that approximately half of the institutions
use E-cadherin expression loss by IHC as an ancillary test to diagnose ILC and that
there is a great variability in immunostaining protocols. This might cause different
staining results and discordant interpretations. As ILC-specific therapeutic and diagnostic
avenues are currently explored in the context of clinical trials, it is of importance
to improve standardization of histopathologic diagnosis of ILC diagnosis.
