LAUSR

BACKGROUND Although identification of human epidermal growth factor receptor 2 (Her2) positive breast cancer represents one of the greatest advances over the past 3 decades, it has not been studied extensively on a national level. METHODS The National Cancer Database is a joint project of the American Cancer Society and the American College of Surgeons and contains data on about 70% of the cancer cases in the United States. Data on Her2 have been collected since 2010 and was used for this study. RESULTS Of 298,937 cases of invasive breast cancer with known Her2 status diagnosed in 2010 and 2011, 43,485 (14.5%) were Her2 positive. Her2 positivity was greatest in Asian/Pacific Islanders and least in non-Hispanic Whites and was markedly more common in younger women. The incidence of Her2 positive tumors ranged from a low of 13.9% in the Mountain West region to a high of 16.0% in the West South Central region (P < .001). Compared with Her2 negative tumors, Her2 positive tumors were larger (2.6 vs 2.2 cm, P < .001), more likely to have positive nodes (39% vs 31% P < .001), have lymphovascular invasion (30% vs 20%, P < .001), and be high grade (56% vs 29%, P < .001). There were also differences by histology: invasive ductal 16.4%, invasive lobular 5.5%, tubular 2.3%, inflammatory 36%, and Paget's with invasion 59%. When adjusted for age, race, tumor size, and nodal status Her2 positive tumors were much more likely to receive chemotherapy (odds ratio = 5.5, confidence interval = 5.2 to 6.0) and somewhat less likely to undergo breast preservation (odds ratio = .78, confidence interval = .76 to .80). CONCLUSIONS Her2 positive tumors have distinct epidemiologic, clinical, and treatment characteristics.