The Status of Breast Cancer Incidence in the United States and Asia

Author (s): Mikayla Chan, Polytechnic School (Pasadena, CA)

Breast cancer is the most common cancer in women worldwide, and Asian women have historically had lower rates of breast cancer compared to their Western counterparts. However, recent studies suggest that this trend may be changing. It has been shown that age-specific incidence rates of invasive breast cancer (BC) up to age 80 among Asian and US white women are similar, suggesting greater similarity in breast cancer rates between Asian populations and American women than previously believed (Sung et al., 2015). Breast cancer emerged as the predominant cancer among Asian women in the United States (Gomez et al., 2017). Another study published in the Journal of the National Cancer Institute in 2020 found that breast cancer rates increased significantly for most Asian American ethnic groups between 1990 and 2014 (Tuan et al., 2020). Interestingly, the rise in breast cancer incidence was primarily driven by statistically significant increases in ER-positive breast cancer rates, while ER-negative rates remained stable or decreased. This suggests that factors related to acculturation or length of residence in the United States may influence breast cancer risk among Asian women. Two San Francisco Bay Area studies comparing breast cancer incidence rates between foreign-born Asian women and United States-born Asian women found that foreign-born Asian women had significantly lower breast cancer incidence rates than United States-born Asian women, suggesting that factors related to acculturation or length of residence in the United States may increase breast cancer risk among Asian women (Morey et al., 2019). Breast cancer risk factors revealed associations primarily in the younger birth cohort, foreign-born women had a marginally increased risk, while foreign-born Chinese women showed a two-fold increase (John et al., 2023). Migration at age 40 or older and longer U.S. residence were associated with a two-fold increased risk. The prevalence of risk factors did not fully explain the observations, suggesting that evolving reproducible and lifestyle-related factors may influence breast cancer risk among Asian American women. The emerging pattern of increasing breast cancer incidence rates in Asian American women shows that more research is needed to demystify the unique risk factors and biology of breast cancer in this population. As Asian American incidence rates approach those of non-Hispanic white women, public health efforts will need to be specific to the needs of Asian American communities.

In recent years, breast cancer trends among Asian women have increased significantly, presenting new challenges in understanding the disease's patterns and risk factors. Breast cancer incidence among Asian women, particularly those in East and Southeast Asia, has exhibited a concerning rise in recent decades, contrary to historical trends. Studies suggest that this surge in incidence, predominantly affecting younger Asian women, is linked to Westernization, characterized by shifts in dietary habits and reproductive behaviors (Lin et al., 2019). Furthermore, contrasting patterns between East Asian and American women underscore racial differences in breast cancer biology. For instance, peak incidence among Asians occurs at ages 45–49, with lower proportions of triple-negative breast cancer but higher proportions of HER2+ tumors observed at younger ages (Gomez et al., 2019). Lifestyle factors such as high fat intake, low vegetable consumption, and delayed childbearing contribute to this trend. Unique genetic factors and molecular signatures further complicate the risk landscape for Asian populations. These findings highlight the need for tailored studies on Asian Americans to address the evolving breast cancer scenario among the population, particularly as incidence rates among Asian Americans intersect with those of non-Hispanic white women in recent data releases.

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