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 < 0.01), while the frequency of peritoneal metastases was significantly higher in the ILC group (68.8%) than in the IDC group (1%) (p = 0.00). Of note, the prognosis after the diagnosis of peritoneal metastases was poor, with a median survival time of 19 ± 9 months and resistance to hormone therapy.

CONCLUSIONS: The extremely high rate (68.8%) of peritoneal metastases was observed in long-term follow-up for the metastatic breast cancer patients with ILC. We need to reveal the definitive feature of ILC and develop new therapeutic strategies to prevent the dissemination of ILCs.