Abstract PS6-20: The 21-gene recurrence score in early non-ductal breast cancer: A national cancer database analysis
Authors: Makower Della , Qin Jiyue , Lin Juan , Xue Xiaonan , Sparano Joseph A 
Published: February 2021

Abstract
Background: The Oncotype DX 21-gene expression assay (ODX) is prognostic for recurrence and predictive of chemotherapy benefit in early estrogen receptor-positive (ER+) HER2-negative (HER2-) breast cancer (BCA). Invasive ductal carcinoma (IDC) comprises approximately 80% of BCA. Invasive lobular carcinoma (ILC) is a subtype of BCA with distinct pathologic features, and often has low to intermediate ODX Recurrence Score (RS). We evaluated differences in clinicopathologic characteristics, RS and chemotherapy benefit between IDC, ILC, and carcinomas of mixed histologies (ductal + lobular (DLC), ductal + other (DOC), and lobular + other (LOC)) in the National Cancer Database (NCDB). Methods: Female patients (pts) diagnosed between 1/1/2010 and 1/1/2014 with ER+ HER2- BCA, measuring up to 5 cm, with 0-3 involved axillary lymph nodes (LN), treated with definitive surgery as first treatment, and with numeric ODX recurrence score (RS) available were identified from the 2005-2016 NCDB database. Associations between categorical variables were examined using the chi-square test. The Cox proportional hazards model was used to examine the difference in overall survival between histology subtypes while controlling for age, race/ethnicity, RS, tumor size, grade, LN involvement and treatment. Results: 77,472 pts met inclusion criteria, 62,395 (83.8%) node negative (N0) and 12,077 (16.2%) node positive (N+). 57,615 pts (77.4%) had IDC; 8693 (11.7%) ILC; 5393 (7.2%) DLC; 2457 (3.3%) DOC; and 312 (0.4%) LOC. DOC and LOC were more common in Black than White pts (p&lt;0.0001). IDC was associated with smaller tumor size and high grade disease. ILC was associated with larger tumor size, and was least likely to be high grade (p&lt;0.0001). IDC was most likely to have high RS &gt;26. Presence of lobular histology (ILC, DLC and LOC) was associated with lower incidence of RS &gt;26. ILC was least likely to have both low RS (0-10) and high RS (p&lt;0.0001). Pts with IDC were more likely to receive adjuvant chemotherapy (27.4%) than pts with other BCA types (ILC 19.3%; DLC 21.9%; DOC 20.5%; LOC 19.2%, p&lt;0.0001). Overall survival (OS) for IDC, ILC and DOC were similar. DLC was associated with improved OS compared with IDC (HR 0.82, p=0.02). Receipt of adjuvant chemotherapy was associated with improved OS in IDC (HR=0.76, p&lt;0.0001) but not in ILC (HR=0.99, p=0.93), DLC (HR=1.04, p=0.86), DOC (HR=0.87, p=0.71), or LOC (HR=2.91, p=0.10). Conclusion: Lobular and mixed BCA histologies have distinct clinicopathologic features compared with IDC, and are less likely to have high RS. OS is similar for early IDC and ILC. Chemotherapy benefit was not seen in ILC or mixed BCA histologies.
Citation Format: Della Makower, Jiyue Qin, Juan Lin, Xiaonan Xue, Joseph A Sparano. The 21-gene recurrence score in early non-ductal breast cancer: A national cancer database analysis [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-20.