The comparison between the two most common histological subtypes of breast cancer – invasive ductal and invasive lobular breast carcinoma.

Introduction: Invasive lobular carcinoma (ILC) occurs in 5–15% of all cases of breast cancer. In most studies, it is found to be more common among older patients, form larger tumours and present with ill-defined margins, in comparison to invasive ductal carcinoma (IDC). Material and methods: Histological preparations were obtained from 651 patients suffering from breast cancer. Preparations stained with hematoxylin and eosin were used to identify tumour type and grading. Samples underwent a basic molecular profile evaluation encompassing ER (oestrogen receptor), PR (progesterone receptor) and human epidermal growth factor receptor 2 (HER2) expression. Results: 592 cases of IDC and 59 cases of ILC were detected. The median age was 60 in both groups. While there were no statistically significant differences between IDC and ILC in nodal status and tumour size for all age groups, IDC was more frequently diagnosed at higher grading (G3). G3 accounted for 32% of all IDC specimens compared to only 13% of ILC specimens. In both groups, the most prevalent combination of hormone receptors was ER+/PR+/HER2-. The differences in ER and PR expression were statistically significant; both were assessed as positive in most ILC cases and just over half of IDC. No HER2 amplification was noted in most cases in both cancer subtypes. Conclusions: In our study, IDC and ILC showed no difference with respect to patients’ median age at the diagnosis and local disease advancement defined by TNM. ILC cases were hormone-dependent and HER2-negative more frequently than IDC. Grade 3 tumours accounted for a higher proportion of IDC cases. This was in line with several other clinicopathological analyses of breast cancer. However, there are also several papers indicating ILC’s association with favourable prognostic features, not only in terms of hormone receptors and HER2 expression but also tumour size and nodal involvement. This underlines the fact that clear differences between IDC and ILC prognosis still cannot be established.