Abstract
BACKGROUND: Breast cancer statistics and clinical trial data largely reflect ductal carcinoma, the dominant histologic subtype, concealing important differences for invasive lobular carcinoma (ILC), the second most common subtype. METHODS: Nationally representative cancer registry data from the National Cancer Institute and Centers for Disease Control and Prevention were used to report on the incidence and outcomes of ILC by age, race, and ethnicity among women in the United States. RESULTS: In 2021 incidence of ILC was 14 per 100,000 women, which accounted for 10.6% of breast cancer diagnoses. Rates increased from 2012 through 2021 in all racial ethnic groups, ranging from 2.5% annually in American Indian/Alaska Native women to 4.4% annually in Asian American/Pacific Islander women. White women have the highest incidence overall (14.7 per 100,000), and in every age group, followed by Black women (11 per 100,000), although American Indian/Alaska Native women have the second-highest rates among those <50. Compared to ductal carcinoma, survival for ILC is slightly higher in the first 7 years after diagnosis and similar at 10 years overall, but lower for ILC for regional- and distant-stage disease, perhaps in part due to its unique metastatic pattern. CONCLUSION: ILC has distinctive characteristics that can contribute to delayed detection, resistance to therapy, and poorer prognosis for advanced disease. Differentiating ILC from ductal carcinoma in research and clinical trials could help identify risk factors, facilitate treatment efficacy, and lead to better understanding of metastatic mechanisms, thus improving outcomes for the increasing number of affected women.