IMPORTANCE: Among older women (aged ≥50 years) with ERBB2 (formerly HER2 or HER2/neu)-positive breast cancer, research has shown racial and ethnic disparities in access to ERBB2-targeted therapies, with Black women receiving treatment at lower rates than their White counterparts. OBJECTIVE: To examine racial and ethnic disparities in receipt of ERBB2-targeted therapies and changes in receipt over time. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study used Surveillance, Epidemiology, and End Results-Medicare linked data from January 1, 2010, to December 31, 2020. Beneficiaries who were diagnosed with ERBB2-positive breast cancer between 2010 and 2019, were aged 66 years or older at diagnosis, were continuously enrolled in Medicare Parts A and B in the 12 months before and after diagnosis, and had localized or regional stage disease at diagnosis were included. Data were analyzed from February through September 2024. EXPOSURE: Race and ethnicity defined as non-Hispanic Black or African American, Hispanic, or non-Hispanic White. MAIN OUTCOME AND MEASURES: The primary outcome was receipt of ERBB2-targeted therapies in the 12 months after diagnosis of ERBB2-positive breast cancer. Modified Poisson regression was used to evaluate the probability of receiving ERBB2-targeted therapy by race and ethnicity. RESULTS: Among 12 765 beneficiaries with ERBB2-positive breast cancer (median [IQR] age, 74 [69-80] years; 99.2% female), 8.1% were of Black, 6.9% Hispanic, and 85.0% White race and ethnicity, and 54.2% received ERBB2-targeted therapy. The overall proportion who received ERBB2-targeted therapies increased from 41.3% in 2010-2011 to 64.3% in 2018-2019. Compared with White patients, Black patients had a lower likelihood of receiving ERBB2-targeted therapies in 2010-2011 (adjusted risk ratio [ARR], 0.81; 95% confidence limit [CL], 0.68-0.97), as did Hispanic patients (ARR, 0.75; 95% CL, 0.62-0.92). Racial and ethnic disparities in receipt of ERBB2-targeted therapies narrowed over time, with no significant differences observed across racial and ethnic groups in 2018-2019 for Black patients (ARR, 0.97; 95% CL, 0.87-1.08) and Hispanic patients (ARR, 1.05; 95% CL, 0.95-1.16). CONCLUSIONS AND RELEVANCE: These findings suggest a narrowing of racial and ethnic disparities in receipt of ERBB2-targeted therapies over time among older Medicare beneficiaries with ERBB2-positive breast cancer. Future research is needed to understand the practices that contributed to the narrowing of racial and ethnic disparities and to develop implementation strategies to effectively improve the quality and equity of breast cancer care.