Comprehensive characterization of invasive mammary carcinoma with lobular features: integrating morphology and E-cadherin immunochemistry pattern

초록

Background & objectives: Invasive lobular carcinoma (ILC) exhibits unique biological behaviours, necessitating accurate diagnosis. In this study, we reviewed breast cancer, with a particular focus on investigating the E-cadherin staining patterns and lobular morphology of cases that were misclassifed in the original reports. Methods: A comprehensive review was conducted on 481 cases diagnosed with invasive breast carcinoma of no special type (IBC - NST) or ILC through biopsy, in which E-cadherin staining was also performed. Subsequently, these cases were categorized into six groups based on a combination of tumour morphology (ductal / lobular) and E-cadherin expression pattern (membranous / loss / aberrant). Results: In 211 cases (43.8%), E-cadherin pattern indicating ILC (loss & aberrant) was observed alongside lobular morphology, representing 5.52% of all breast cancer biopsies during the relevant period. 181 cases (37.6%) showed membranous pattern with ductal morphology, 4 (0.8%) were mixed IBC-NST and ILC, and 85 (17.7%) exhibited discordance between morphology and E-cadherin. Notably, of 58 cases reviewed as ILC due to aberrant pattern, only 15 (25.9%) had initial ILC diagnosis. Among 58 cases showing membranous pattern with lobular morphology, only 2 were diagnosed as ILC in the original reports. Similarly, despite the presence of ductal morphology, 17 cases (63%) exhibiting either loss or aberrant pattern were initially diagnosed as ILC. Conclusion: Despite the E-cadherin expression pattern being recognized as a ‘desirable’ diagnostic criterion for ILC in the WHO blue book, real-world practice tends to depend on E-cadherin results, even in the presence of evident lobular morphology. Especially, aberrant pattern was often interpreted as membranous pattern, leading to misdiagnoses of IBC-NST. Additionally, cases showing discordance between morphology and E-cadherin patterns were observed in 85 cases (17.7%), highlighting the need for molecular clarifcation of these discrepancies.