Background: The aim of this study was to compare clinical and pathological outcomes after neoadjuvant chemotherapy between oestrogen receptor (ER)-positive invasive pure lobular carcinoma (ILC) and invasive ductal carcinoma (IDC).
Methods: This analysis included 1895 patients (n=177 ILC; n=1718 IDC), with stage I-III breast cancer, who received neoadjuvant chemotherapy. Clinical and pathological response rates, the frequency of positive surgical margins and rate of breast-conserving surgery were compared.
Results: There was a trend for fewer good clinical responses in ILC compared with IDC. Tumour downstaging was significantly less frequent in ILC. Positive or close surgical resection margins were more frequent in ILC, and breast-conserving surgery was less common (P<0.001). These outcome differences remained significant in multivariate analysis, including tumour size, nodal status, age, grade and type of chemotherapy. Invasive pure lobular carcinoma was also associated with a significantly lower pathological complete response (pCR) rate in univariate analysis, but this was no longer significant after adjusting for tumour size and grade.
Conclusion: Neoadjuvant chemotherapy results in lower rates of clinical benefit, including less downstaging, more positive margins and fewer breast-conserving surgeries in ER-positive ILC compared with ER-positive IDC. Pathological complete responses are rare in both groups, but do not significantly differ after adjusting for other variables.