Specific sites of metastases in invasive lobular carcinoma: a retrospective cohort study of metastatic breast cancer

Background Invasive lobular carcinoma (ILC) is known to be the second most common histological type following invasive ductal carcinoma (IDC). Definitive clinical features of ILC are controversial. Methods We retrospectively analyzed a cohort of 330 patients with metastatic breast cancer, 303 of IDC, 19 of ILC, and 8 of others. We compared the patient age and tumor–node–metastasis factors, disease-free survival (DFS), estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) expression at the primary site between ILC and IDC. We then selected the patients in the ER + or PR + /HER2 − subtype specifically and compared sites of recurrence, and the survival curve starting from the point of development of metastatic disease. Results The clinical stage was significantly higher in the ILC patients than in the IDC ( p = 0.001). The mean (±SD) of DFS for the ILC and IDC patients was 2.6 ± 0.6 and 2.4 ± 0.3 years, respectively, with no significant difference ( p = 0.18). However, the hormone receptor status was same between both groups; the rate of HER2 positivity was significantly lower in the ILC group (0%) than in the IDC group (16.2%) ( p = 0.05). In ER + or PR + /HER2 − subtype, the mean DFS for the ILC and IDC was 2.9 ± 0.6 and 3.1 ± 0.3 years, and the median survival time after the recurrence for ILC and IDC patients was 4.2 ± 0.7 and 5.6 ± 0.7 years, respectively, with no significant difference ( p = 0.77). The frequency of lung metastases was significantly lower in the ILC group (6.3%) than in the IDC group (53.7%) ( p