Resident University of Minnesota Minneapolis, Minnesota, United States
Disclosure: Disclosure information not submitted.
Participants should be aware of the following financial/non-financial relationships:
Saranya Prathibha, MD: Disclosure information not submitted.
Introduction: Invasive lobular carcinoma (ILC) has been shown to be less chemo-responsive with poorly described survival rates compared to invasive ductal cancer (IDC). HER2 positivity is rare but does occur in the setting of ILC. We sought to determine the effects of HER2 positivity on oncologic outcomes in breast cancer patients with ILC.
Methods: Patients with stage I-III HER2+ ILC and IDC were identified from the National Cancer Database (2010-2017) and compared using Pearson’s chi-squared test, Cochrane Armitage test for trend, and a logistic regression model by tumor, patient, and treatment characteristics. Overall survival was analyzed with the Kaplan-Meier method and a Cox proportional hazard model that included age, race, Charlson comorbidity index (CCI), year of diagnosis, tumor stage, tumor grade, progesterone receptor positivity, and treatment (chemotherapy, radiation).
Results: We identified 4798 patients with HER2+ ILC and 134904 with HER2+ IDC. Compared to patients with IDC, patients with ILC were older (≥65 years 46% vs IDC 29%, p< 0.0001), and non-Hispanic white (80% vs 71%, p< 0.0001), but had similar CCI (p=0.30). ILC were more likely to be PR positive, lower grade, and larger in size, but ILC and IDC had similar nodal positivity rates (Table 1). Most of the identified ILC were pleomorphic (58.9%). Patients with ILC had a worse overall survival compared to those with IDC (5-year overall survival ILC 89% vs IDC 91%, p=0.0003). Only 72% of ILC and 79% of IDC patients received chemotherapy. Over time, chemotherapy use increased for ILC (Δ9.84% p < 0.0001). Chemotherapy positively impacted overall survival for both ILC and IDC (HR 0.74, p< 0.05).
Conclusions: HER2+ ILC confers a worse prognosis than HER2+ IDC despite having lower tumor grades and increased PR positivity. Unlike for HER2- ILC and similar to HER2+ IDC, chemotherapy did improve overall survival for patients with HER2+ ILC. Emphasis should be placed on improving rates of chemotherapy delivery to these patients.
Learning Objectives:
better understand the survival impact of HER2 positivity on invasive lobular carcinoma.
further describe tumor characteristics of HER 2 positive invasive lobular carcinoma.
understand optimal treatment modalities for HER2 positive invasive lobular carcinoma.
