Adjuvant chemotherapy in patients with invasive lobular carcinoma and use of the 21‐gene recurrence score: A National Cancer Database analysis

Background Invasive lobular carcinoma (ILC) is traditionally considered less responsive to chemotherapy. Although the Oncotype recurrence score (RS) has been validated to identify high‐risk patients who benefit from chemotherapy, some studies have questioned its relevance in patients with ILC. The objective of this study was to better characterize potential use of the RS in these patients. Methods The National Cancer Database was used to identify women with stage I through III, T1 through T3, N0 or N1, hormone receptor‐positive, HER2‐negative ILC or invasive ductal carcinoma (IDC) who had an available RS between 2010 and 2016. Multivariable Cox regression was used to model the effect of variables on 5‐year overall survival (OS). The Kaplan‐Meier method was used to estimate OS according to the RS, nodal status, and chemotherapy. Results In total, 15,763 patients with ILC and 100,070 with IDC were identified. The mean age of patients with ILC and IDC was 59.2 ± 9.1 and 57.2 ± 9.8, respectively. A lower percentage of patients with ILC versus those with IDC had a high RS, defined as >25 (6.6% vs 16.0%; P