Although breast cancer rates in the U.S. seem to have plateaued or even declined over the past 2 decades, the same may not be true for some minority patient populations—including immigrant Asian American women, according to new research (Prev Chronic Dis 2019; doi:10.5888/pcd16.180221).
“These populations have often been overlooked in population-based studies of breast cancer risk,” explained the study's lead author Brittany N. Morey, PhD, MPH, a postdoctoral researcher at the University of California, Riverside. “Although historically Asian American women have had lower rates of breast cancer than the general U.S. population, over the past 20 years these rates have been increasing rapidly in many Asian American groups.”
Such a disparity led Morey and her team to take a close look at three Asian American groups: U.S.-born, and immigrants who have lived either less than or more than 50 percent of their life in the U.S.
They drew the study cohort from the San Francisco Bay Area, which is home to the second highest concentration of Asian American in the U.S. (behind Hawai'i), at 29 percent of the area's population.
Using the Greater Bay Area Cancer Registry, the researchers identified 570 Asian American women, 132 cases and 438 controls. Of those 132 cases, 17 percent were U.S.-born and 42 percent were immigrants who had been in the U.S. for at least 50 percent of their lives.
The participants were 53 percent Chinese, 20 percent Filipina, and 27 percent other Asian American ethnicity. Ages ranged from 22 to 87. The researchers collected data using telephone interviews and self-administered questionnaires.
The data show that, compared with the U.S.-born group, those who lived more than 50 percent of their life in U.S. were, on average, three times as likely to have breast cancer; those who lived less than 50 percent of their life in U.S. were 2.46 times as likely, on average.
Living longer in the U.S. did not translate to a statistically significant increase in the risk of breast cancer, contrary to the researchers' hypothesis and previous research. In addition, the increased risk of breast cancer in immigrant Asian American women remained, even after accounting for modifiable risk factors such as pregnancy history, hormone replacement therapy, and body mass index.
Secondary study findings support previous research, with similar breast cancer risks among Asian American women such as higher socioeconomic status, having the first child at 35 or older, having a family history of breast cancer, and premenopausal status.
The main findings come as something of a surprise to researchers, considering previous studies leading into the 2000s found breast cancer was higher among U.S.-born women than among immigrant women.
“Our study found in a recent cohort of Asian American women in the San Francisco Bay Area that this trend may be shifting, such that breast cancer risk is higher among Asian American women who are immigrants compared with those who are U.S.-born,” Morey noted. “This may be because immigrant Asian American women are arriving to the U.S. with higher breast cancer risk than in previous cohorts.
“Studying what might be causing these rising rates among Asian Americans informs us more about breast cancer in this patient population, and also informs us more broadly about which risk factors place women at higher risk for breast cancer,” Morey explained.
Although the breast cancer incidence is high in North America and relatively low in Asia, the risk is rapidly increasing for East and Southeast Asian countries. The demographics of immigration may also play into the changing cancer risk, and Morey and her team speculate that the “Asian American immigrant population in the San Francisco Bay Area may reflect trends among populations in Asia.”
With today's immigration policies, Asian immigrants are more skilled and may come from a higher socioeconomic status, measured by education and median household income, than in previous decades. Only 20 percent of all immigrants were college-educated in 1970—51 percent were in 2013. More recent income comparisons show 42 percent of naturalized Asian Americans in the Bay area had a household income greater than $135,000 in 2016, while only 18 percent made that much in 2005.
Many of the lifestyle related to a higher socioeconomic status—such as increased screening, lower parity, delayed childbirth, decreased breastfeeding, and sedentary lifestyles—also increase breast cancer rates. This means today's immigrant Asian American women are likely entering the U.S. with a higher risk of breast cancer than in the past.
The study has several limitations that warrant further study, including its relatively small sample size and case-control design.
The cases and controls were matched according to country of origin, so the researchers were unable to examine any differences based on various Asian American subpopulations.
And while the San Francisco Bay Area provided a robust Asian American population to work with, its unique characteristics make it harder to generalize study findings to the larger U.S. population. Research with larger samples in broader geographic areas will help corroborate the findings, Morey admits.
Still, the data should help clinicians better understand their patients' risk status based on their ethnicity.
“Clinicians should be aware of immigrant status in patient history taking,” Morey clarified. “There may be an increased need for breast cancer treatment services for immigrant Asian American women who are likely to need greater in-language support and culturally sensitive treatment options. Overall, there is a need for continued efforts to increase access to mammograms among all Asian American women, both U.S.-born and foreign-born.”
Rebecca Hepp is a contributing writer.