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Breast cancer rates are rapidly increasing among Asian women in California


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The majority of racial groups in the United States have seen declines in breast cancer rates. However, this study provides new insights into the patterns of breast cancer rates in Asian American subgroups in California. Using 26 years of data, this research found that breast cancer is rapidly increasing among this population, contrasting to a decline in rates among non-Hispanic white women in California and nationwide. (8/15/17)


STUDY AT A GLANCE

This study is about:

The rapidly increasing rate of breast cancer among Asian women in California.

Why is this study important?

Although other racial groups in the United States have reported declines in breast cancer rates, breast cancer among Asian Americans appears to be increasing, and it is not known why. This pattern of increase is important because it suggests that unexpected public health differences, such as access to screening and care, exist for this population. 

Study findings: 

From 1988 to 2013, 548,259 new cases of breast cancer were diagnosed in women living in California including 383,478 in non-Hispanic Caucasians (NHW) and in 45,721 Asian Americans (AA). 

Using this data, this study determined breast cancer rates for Asian American women as a single group and by seven major ethnicities: Chinese, Japanese, Korean, Filipino, Vietnamese, South Asians (Asian Indians and Pakistanis), and Southeast Asians (Cambodians, Laotians, Hmong, and Thai). 

  • As a single group, Asian American women experienced a rapid increase in breast cancer rates compared to non-Hispanic Caucasian women (NHW breast cancer rates actually declined in California and nationwide during this time).
    • Rates increased across all major ethnic groups except Japanese.
    • The largest increase was seen in Koreans (1988-2006) and Southeast Asians (1988-2013).
  • Among Asian American women younger than age 50, the largest increases occurred in in Vietnamese and other Southeast Asians.
  • Among Asian American women over age 50, increases were seen in all AA ethnics groups.

What does this mean for me?

This study indicates that breast cancer rates in Asian Americans living in California are rapidly increasing. The results suggest that documenting breast cancer trends for major Asian American ethnic minority groups can contribute to a better understanding why the increase occurred, help target prevention and screening efforts, and guide future research into specific risk factors for each group.  These results highlight that there is value and important insight gained when studying distinct ethnicities.

Though more work needs to be done to understand why this increase is happening, as the study authors write, “Culturally tailored efforts to increase awareness of and attention to breast cancer risk factors are needed.” Asian Americans should work with their health care provider to determine the best time to start breast cancer screening and the optimal screening schedule. As with all women, it’s important for Asian Americans to know their family history of cancer and speak with a genetics expert if there are any signs of hereditary cancer in their family.

Questions to ask your health care provider:

  • When should I start getting screened for breast cancer?
  • How often should I get screened for breast cancer?
  • How can I lower my breast cancer risk?
  • Are you aware of my family history of cancer?

 

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.”

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Posted 8/15/17

References

Gomez SL, Von Behren J, McKinley M, et al. “Breast cancer in Asian Americans in California, 1988-2013: increasing incidence trends and recent data on breast cancer subtypes.” Breast Cancer Res Treat (2017) 164:139-147.

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