Trends in Disparities and Transitions of Treatment in Patients With Early Breast Cancer in China and the US, 2011 to 2021

IMPORTANCE: Breast cancer treatment has profoundly improved in China recently. However, trends in disparities and transitions of treatment in early-stage cancer between China and the US are not well known. OBJECTIVE: To identify changes for patients with early breast cancer by using large databases from China and the US. DESIGN, SETTING, AND PARTICIPANTS: This multicenter cross-sectional study used the Chinese Society of Clinical Oncology Breast Cancer (CSCO BC) database from hospitals in 13 provinces in China and the Flatiron Health (hereinafter referred to as Flatiron) database from more than 280 community oncology clinics in the US. Patients with stage I to III breast cancer diagnosed from January 1, 2011, to December 31, 2021, were included. Data were analyzed from June 10 to December 1, 2022. MAIN OUTCOMES AND MEASURES: The distribution of age, clinical stage, and cancer subtypes at diagnosis were examined overall and by year. The mean annual percent change (MAPC) from 2011 to 2021 in systemic therapy and surgery was also analyzed. RESULTS: A total of 57 720 patients with early breast cancer were screened from the CSCO BC (n = 45 970) and Flatiron (n = 11 750) databases. The median age at diagnosis in China among the 41 449 patients included in the age analysis was 47 (IQR, 40-56) years; in the US, the median age was 64 (IQR, 54-73) years. Among patients with clinical stage data in the CSCO BC (n = 22 794) and Flatiron (n = 4413) databases, the proportion of stage I cancer was 7250 (31.8%) vs 2409 (54.6%); stage II cancer, 10 043 (44.1%) vs 1481 (33.6%); and stage III cancer, 5501 (24.1%) vs 523 (11.9%). The proportion of hormone receptor–positive cancer in China was 69.8%, lower than that in the US (87.5%). For patients with ERBB2 (formerly HER2 or HER2/neu)-positive cancer, the proportion in China (30.2%) was higher than that in the US (15.6%). For neoadjuvant therapy, the annual rate increased from 247 of 1553 (15.9%) to 200 of 790 (25.3%) in China, with an MAPC of −4.4% (95% CI, −50.6% to 85.0%; P = .89). For patients with ERBB2-positive cancer, the proportion treated with trastuzumab in early-stage cancer in China increased significantly, with an MAPC of 22.1% (95% CI, 17.4%-26.9%; P < .001), and overtook that in the Flatiron database since 2017 (1684 [68.5%] vs 550 [62.5%]; P < .001). CONCLUSIONS AND RELEVANCE: The findings of this cross-sectional study suggest that disparities in treatment of early breast cancer narrowed between China and the US during the study period. The rapid growth of trastuzumab treatment in China was suggestive of differential access to targeted ERBB2 therapy.