The role of histological subtype in hormone receptor positive metastatic breast cancer: similar survival but different therapeutic approaches

Introduction: This study describes the differences between the two largest
histological breast cancer subtypes (invasive ductal carcinoma (IDC) and invasive
(mixed) lobular carcinoma (ILC) with respect to patient and tumor characteristics,
treatment-choices and outcome in metastatic breast cancer.
Results: Patients with ILC were older at diagnosis of primary breast cancer and
had more often initial bone metastasis (46.5% versus 34.8%, P = 0.01) and less
often multiple metastatic sites compared to IDC (23.7% versus 30.9%, P = 0.11).
Six months after diagnosis of metastatic breast cancer, 28.1% of patients with ILC
and 39.8% of patients with IDC had received chemotherapy with a longer median
time to first chemotherapy for those with ILC (P = 0.001). After six months 84.8%
of patients with ILC had received endocrine therapy versus 72.5% of patients with
IDC (P = 0.0001). Median overall survival was 29 months for ILC and 25 months for IDC (P = 0.53).
Materials and Methods: We included 437 patients with hormone receptorpositive
IDC and 131 patients with hormone receptor-positive ILC, all diagnosed with
metastatic breast cancer between 2007–2009, irrespective of date of the primary
diagnosis. Patient and tumor characteristics and data on treatment and outcome were collected. Survival curves were obtained using the Kaplan-Meier method.
Conclusions: Treatment strategies of hormone receptor-positive metastatic
breast cancer were remarkably different for patients with ILC and IDC. Further
research is required to understand tumor behavior and treatment-choices in real-life