Survival Outcomes in Invasive Lobular Carcinoma Compared to Oestrogen Receptor-Positive Invasive Ductal Carcinoma

SIMPLE SUMMARY: Around 10–15% of breast cancer diagnoses are invasive lobular cancers (ILC), and they are currently treated in a similar way to the more common invasive ductal cancer (IDC), although they display different characteristics. The main objective of this study was to identify any differences in outcome following chemotherapy treatment between ILC and oestrogen receptor-positive (ER+) and human epidermal growth factor receptor 2-negative (HER2−) IDC. Results from the analysis show worse survival in patients with ER+HER2− ILC after chemotherapy compared to ER+HER2− IDC, even after correcting for tumour size, grade, age, and nodal involvement at presentation, suggesting a worse response to chemotherapy in ILC. Thus, recommendations for chemotherapy treatment should be considered separately for the two subtypes. However, this association should be studied in a larger population to confirm this finding. ABSTRACT: Invasive lobular breast cancer (ILC) accounts for 10–15% of breast cancers and has distinct characteristics compared with the more common invasive ductal carcinoma (IDC). Studies have shown that ILC may be less sensitive to chemotherapy than IDC, with lower rates of complete pathological response after neo-adjuvant chemotherapy, but it is not clear how this affects long-term survival. Patients at Guy’s and St Thomas’ NHS Foundation Trust between 1975 and 2016 diagnosed with ER+ IDC or ER+ ILC were eligible for inclusion. Kaplan–Meier plots and Cox proportional-hazards regression models were used for analysis. There was no difference in overall survival comparing ER+ ILC to ER+ IDC (OR: 0.94, 95% CI: 0.83, 1.04) with a median follow-up time of 8.3 years compared to 8.4 years in IDC. However, ER+HER2− ILC had worse survival compared to ER+HER2− IDC in those that received chemotherapy (OR: 1.46, 95% CI: 1.06, 2.01). Here, median follow-up time was 7.0 years in ILC compared to 8.1 years in IDC. These results indicate worse overall survival after chemotherapy (neo-adjuvant and adjuvant) in ILC compared to ER+HER2− IDC even when correcting for tumour grade, age, size, and nodal involvement, but validation is needed in a larger study population.