Abstract P1-13-06: Does histological subtype play a role in treatment decision-making for hormone receptor positive metastatic breast cancer? A study of the Southeast Netherlands breast cancer consortium
Authors: Lobbezoo DJA , Truin W , Voogd AC , Roumen RMH , Vreudgenhil G , Dercksen MW , van den Berkmortel F , Smilde TJ , van de Wouw AJ , van Kampen RJW , van Riel JMGH , Peters NAJB , Peer PGM , Tjan-Heijnen VCG 
Published: May 2016

Abstract
Introduction
Breast cancer is a heterogeneous disease with distinct biological subtypes. Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the two most frequent histological breast cancer subtypes. With this study, we aimed to provide insight into the role of histological subtype on the characteristics, choices with respect to systemic therapy in daily practice and outcome of patients with metastatic breast cancer.
Patients and methods
We analyzed 815 patients diagnosed with metastatic breast cancer in eight hospitals between 2007 and 2009. All hormone receptor (HR) positive patients with either IDC or (mixed) ILC were included. Patient and tumor characteristics, outcomes and treatment data were collected. Survival curves and time to first palliative systemic therapy (either chemotherapy or endocrine therapy) were estimated using the Kaplan-Meier method and compared using log-rank tests. To explore the association of palliative systemic therapy with the survival of patients with metastatic breast cancer a Cox proportional hazards model was performed with palliative chemotherapy and endocrine therapy as a time-dependent covariates.
Results
A total of 568 patients with HR-positive tumors were included; 437 with IDC and 131 with (mixed) ILC. Patients with ILC were older at diagnosis of primary breast cancer, had larger primary tumors and more node-positive disease compared with IDC. Median survival was not different between the subtypes (29 months for ILC and 25 months for IDC, P=0.53).
One year after diagnosis of metastatic breast cancer, less patients with HR-positive ILC received chemotherapy (33% of patients with ILC and 47% of patients with IDC) and their time to first palliative chemotherapy was significantly longer compared with HR-positive IDC (P=0.001). Time to first palliative endocrine therapy was significantly shorter for ILC compared with IDC (P=0.0001).
In multivariable analysis for patients with ILC with palliative endocrine therapy and palliative chemotherapy as time-dependent covariates, palliative chemotherapy as first given systemic therapy was associated with an unfavorable outcome (hazard ratio 2.8, 95% CI 1.7-4.6, P&lt;.0001) compared to no palliative chemotherapy and treatment with palliative endocrine therapy as first given systemic therapy was associated with a favorable outcome (hazard ratio 0.4, 95% CI 0.2-0.8, P=0.005). In multivariable analysis for patients with IDC, treatment with palliative chemotherapy as first given systemic therapy was also associated with unfavorable outcome (hazard ratio 2.1, 95% CI 1.6-2.7. P&lt;.0001), whereas treatment with palliative endocrine therapy as first given systemic therapy was not associated with outcome for patients with IDC (hazard ratio 0.9, 95% CI 0.6-1.2, P=0.4).
Conclusion
There was no difference in survival of metastatic breast cancer patients with HR-positive ILC compared with those with IDC. This similar outcome was achieved with different treatment strategies, in which patients with ILC were more likely to receive endocrine therapy and less likely to receive chemotherapy.
Citation Format: Lobbezoo DJA, Truin W, Voogd AC, Roumen RMH, Vreudgenhil G, Dercksen MW, van den Berkmortel F, Smilde TJ, van de Wouw AJ, van Kampen RJW, van Riel JMGH, Peters NAJB, Peer PGM, Tjan-Heijnen VCG. Does histological subtype play a role in treatment decision-making for hormone receptor positive metastatic breast cancer? A study of the Southeast Netherlands breast cancer consortium. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-13-06.