Breast cancer is surging among Asian American women — and scientists don’t know why

Breast cancer rates have climbed across nearly every Asian American ethnic group at a pace that exceeds increases seen in any other U.S. ethnic group. The trend is particularly pronounced among women under 50 and among those diagnosed with advanced disease or certain aggressive forms of breast cancer.

Breast Cancer Rates Are Climbing Quickly

The study, published in JAMA Network Open, found that breast cancer incidence rose by more than 3% annually in nearly every Asian American ethnic group examined. The increases were even greater among Chinese and Vietnamese women.

Native Hawaiian women already have some of the highest breast cancer rates among women in the United States. However, their rates increased by about 1% per year, substantially less than the increases observed among Asian American groups.

Researchers say greater use of breast cancer screening probably does not explain the trend. Screening tends to identify more cancers at earlier stages, yet the fastest increases occurred among cancers that had already spread.

One particularly concerning finding involved triple-negative breast cancer, which is considered the most aggressive subtype. Among Chinese American women, cases of triple-negative breast cancer increased by more than 6% each year between 2017 and 2022.

“These patterns are highly concerning from a disparities standpoint,” said senior author Scarlett Lin Gomez, PhD, professor of epidemiology and biostatistics at UCSF and co-leader of the Cancer Control Program at the UCSF Helen Diller Family Comprehensive Cancer Center. “They underscore why it is so important to move beyond treating Asian Americans, Native Hawaiians, and Pacific Islanders as a single population.”

A Closer Look at Breast Cancer Risk

To examine these trends, researchers analyzed about 150,000 invasive breast cancer cases diagnosed from 2000 through 2022. The data came from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program.

The analysis included nine specific Asian American, Native Hawaiian, and Pacific Islander (AANHPI) populations across 14 states. Together, those states are home to about two-thirds of the U.S. AANHPI population.

Historically, Asian American women, with the exception of Native Hawaiian women, have had lower breast cancer rates than non-Hispanic white women. That difference is now shrinking quickly. By 2022, breast cancer incidence among Asian American women under 50 had become comparable to the rate among white women of the same age group.

Why Breast Cancer Is Rising Remains Unclear

Researchers do not yet know what is driving the increase in breast cancer among women younger than 50.

Changes in reproductive patterns, diet, and other lifestyle factors may contribute to the trend, but the research team said those factors do not fully account for what they are seeing.

Some Asian American communities may also face risk factors that scientists have not yet identified. Researchers hope two UCSF-based projects, the CRANE breast cancer study and the ASPIRE cohort study, will help uncover additional explanations.

“Understanding why breast cancer is increasing so rapidly in these communities is critical,” Gomez said. “At the same time, we need to ensure that women across all Asian American, Native Hawaiian, and Pacific Islander communities have access to culturally appropriate education, screening, and timely follow-up care.”

Authors: Other UCSF authors are Meg McKinley, MPH; Katherine Lin, MPH; Iona Cheng, PhD; and Salma Shariff-Marco, PhD.

Funding: The Breast Cancer Research Foundation, the National Cancer Institute’s SEER Program, and the Surveillance Research Program Division of Cancer Control and Population Sciences of the National Cancer Institute.