Study: Breast cancer rates are rapidly increasing among Asian women in California

IN-DEPTH REVIEW OF RESEARCH

Study background:

Over the past 15 years, breast cancer rates have either stayed the same or decreased in most US populations. However, rates are increasing in Asian Americans. Scarlett Lin Gomez, PhD, M.P.H. and her colleagues from Stanford Cancer Institute and the Cancer Prevention Institute of California published work in Breast Cancer Research and Treatment in July 2017 reporting breast cancer rates in different Asian American ethnicities between 1988 and 2013 in California. This research indicates that to better understand factors that are contributing to increased risk in Asian Americans, it is important to study individually the different Asian ethnicities.

Researchers of this study wanted to:

Better understand what factors may be contributing to the rapid rise in breast cancer rates in Asian Americans.

Population(s) looked at in the study:

The authors studied breast cancer trends by age and stage from seven Asian American ethnic groups in California from 1988 to 2013, and patterns of breast cancer subtypes and age at diagnosis form 2009-20013. Researchers used data from the California Cancer Registry (CCR), which includes four National Cancer Institute Surveillance, Epidemiology and End Results (SEER) databases.

Seven major Asian American ethnicities studied: Chinese, Japanese, Korean, Filipino, Vietnamese, South Asians (Asian Indians and Pakistanis), and Southeast Asians (Cambodians, Laotians, Hmong, Thai). The data from these groups were compared to non-Hispanic whites (NHW).

Study findings: 

• Asian Americans as a group experienced a larger increase in breast cancer compared to NHW:
  • Rates increased from 1988 to 1998 compared to NHW women from 1988 to 2001.
  • Rates increased modestly, while rates for NHW woman fluctuated somewhat from 1998 to 2013.
• Breast cancer rates increased significantly from 1988 to 2013 for women of Chinese, Filipino, Korean, South Asian, Vietnamese, and Southeast Asian descent:
  • Rates did not increase for Japanese women during this time.
  • The largest rate increase was among Korean and Southeast Asian women between 1988 and 2006.
• Among Asian American women younger than 50 years old breast cancer rates increased for all women except for Japanese, Filipina and South Asians:
  • The largest increases occurred in Korean, Vietnamese, and Southeast Asian women.
• Among Asian American women over age 50, increases were seen in all ethnics groups:
  • The largest increases were seen in Japanese women from 1988 to 1998, in Korean women from 1988 to 1997, and in South Asian women from 1990-1996.
  • Rates among older Japanese women have been generally stable in more recent years.
• Considering stage at diagnosis, increases occurred among all Asian American women for localized and distant stage disease, while rates were stable for regional disease and decreased for unstaged tumors:
  • Rates for distant-stage disease increased most for Filipina women.
• Compared to NHW women, Filipina and Vietnamese women had higher rates of some HER2+ subtypes:
  • Young (under 50) and older (over 50) Filipina women had the highest rates of ER/PR-negative/HER2-positive breast cancer compared to NHW women.
• The breast cancer rate for the triple-negative breast cancer (TNBC) subtype among all Asian American ethnicities combined was slightly lower compared to NHW:
  • Young South Asian women and older Japanese women, however, had TNBC rates similar to NHW.

Limitations:

While this research study confirms what others have observed-that breast cancer rates are increasing in Asian American women-this study has limitations. Because it only included women from California, researchers do not know whether the results can be generalized to Asian American women in other areas of the US. Additionally, there is the possibility of misclassification of ethnicity, though the study authors state that “Misclassification of ethnicity is fairly minimal in cancer registry data.”  Furthermore, the number of cases with an unknown breast cancer subtype was high, due mostly to unknown HER2 status. This could have resulted in under-estimation of the rates of different breast cancer subtypes in the Asian American population. Finally, tumor subtyping results may differ because this study combined data that used older methods to subtype breast cancers with newer data that used more advanced techniques. In the past pathologists looked at proteins within the tumor. Newer techniques categorize tumor subtypes based on expression of genes.                  

Conclusions:

This study confirms that breast cancer rates in Asian American women are increasing. More work needs to be done to understand the factors that are contributing to this increase.  However, the authors state that “Culturally tailored efforts to increase awareness of and attention to breast cancer risk factors are needed.”

Share your thoughts on this XRAYS article by taking our brief survey

Posted 8/15/17