Differences in Histological Subtypes of Invasive Lobular Breast Carcinoma According to Immunohistochemical Molecular Classification.

The technical complexity of gene expression profiling in routine practice has necessitated the use of surrogate molecular classification of breast cancer, based on immunohistochemical analyses. BACKGROUND AND OBJECTIVES: The aim of this study was to compare the differences between histological and molecular subtypes of invasive lobular carcinoma (ILC) of the breast, in order to be able to predict the behavior and prognosis of the disease, as well as to effectively determine therapy. MATERIAL AND METHODS: This study included 263 cases of breast ILC diagnosed over a seven-year period. The diagnosis of invasive lobular carcinoma is based on the characteristic growth pattern and phenotype of cancer cells with the respective subtypes: classic, alveolar, solid, tubulolobular, pleomorphic and mixed lobular type. The examined cases were divided into five groups according to molecular classification based on the expression of ER, PR, HER2 and Ki67 immunohistochemical markers. RESULTS: It was found that the pleomorphic subtype occurred statistically significantly less often as the luminal A subtype compared to others (p = 0.00027), and the HER2-enriched subtype occurred statistically significantly more often in the pT4 stage (p = 0.024). CONCLUSIONS: The results of this study significantly singled out the luminal A subtype, and among them classic ILC, as the subtype with the most favorable expression ratio of the investigated predictive/prognostic immunohistochemical markers.