Skip to main content

Women who identified as American Indian or Alaska Native were less likely than women of other racial and ethnic groups to start hormone therapy for breast cancer after surgery and stay on the treatment for the recommended five years, a new study from the Kaiser Permanente Division of Research shows.

A smiling man with short dark hair stands in front of a stone wall, arms crossed in a relaxed pose. He is a wearing a striped long-sleeved shirt.
Marc Emerson, PhD, MPH, is a UNC Lineberger postdoctoral fellow and the study’s lead author.

The study published in the journal Cancer is believed to be the first to look at hormone therapy initiation and adherence in American Indian and Alaska Native women diagnosed with breast cancer. It included a racially diverse group of 23,680 women in Kaiser Permanente Northern California (KPNC) diagnosed with early-stage hormone-sensitive breast cancer between 1997 and 2014. This is the most common type of breast cancer.

The research showed that hormone therapy initiation rates were 78% for Black women, 78.6% for American Indian/Alaska Native women, 82.5% for white women, 83% for Hispanic women, and 84.7% for Asian/Pacific Islander women. After five years, 50.8% of American Indian/Alaska Native women remained on treatment, compared to 53.4% of Black women, 53.8% of Hispanic women, 58.8% of white women, and 63% of Asian/Pacific Islander women.

“There are previous studies, including some by researchers at the Division of Research, that show a marked drop off in endocrine therapy use over time, so, that wasn’t surprising to see,” said the study’s senior author Laurel Habel, PhD, a senior research scientist at the Division of Research. “The disparities we found indicate that further research is needed on modifiable factors that contribute to adherence that might differ by race and ethnicity.”

From 2013 to 2017, the breast cancer death rate in the U.S. fell for women of all races and ethnicities, except for American Indian and Alaska Native women. Previous studies have found that factors such as a tumor’s biology, how far the cancer has spread, access to breast cancer screening, and health insurance coverage can explain some ­— but not all — of these disparities.

The research team carried out this study to see whether differences in rates of hormone therapy initiation and adherence might also be a factor in the higher death rates seen in American Indian and Alaska Native women. Of the 23,680 women in the study, 16,677 were white, 3,066 were Asian/Pacific Islander, 2,355 were Hispanic, 1,484 were Black, and 98 were American Indian/Alaska Native. The researchers used data from the KPNC cancer registry to identify the breast cancer patients. They used information from the KPNC Pharmacy Information Management System, which tracks ordered and filled prescriptions, to assess hormone therapy use.

“Urban American Indian and Alaska Native women are often not included in larger cancer studies,” said the study’s lead author Marc Emerson, PhD, MPH, a postdoctoral fellow in epidemiology at the UNC Lineberger Comprehensive Cancer Center. “The data from Kaiser Permanente Northern California made it possible to place these women’s endocrine therapy initiation and adherence in the context of that seen in other racial and ethnic groups.”

Guidelines recommend that women with early-stage, hormone-sensitive breast cancer be treated with hormone therapy (also called endocrine or anti-estrogen therapy) for five to 10 years after surgery. These treatments, which include tamoxifen and a class of drugs called aromatase inhibitors, are taken in pill form, daily. Clinical trials have shown that these therapies reduce a woman’s risk of dying from breast cancer by 30% or more. However, previous studies by the Division of Research have found women often stop taking the medication due to treatment-related side effects such as hot flashes, bone and joint pain, depression, sleep problems, and nausea and vomiting.

“Ensuring continual adherence to hormone therapy, especially aromatase inhibitors, can be challenging,” said Marilyn Kwan, PhD, a senior research scientist at the Division of Research who has studied this issue extensively. “Our previous work has found that 45% of over 3,200 women diagnosed at Kaiser Permanente Northern California from 2005 to 2013 started on an aromatase inhibitor and then switched to tamoxifen due to mainly bone and joint pain, but then 24% went on to completely discontinue therapy. We found in other work that personal and clinical social support may play an important role in helping breast cancer patients initiate and remain adherent to their hormone therapy.”

The new study included only women who had health insurance and who lived in an urban setting. “This represents a best-case scenario for accessing health care, and still rates of hormone therapy were lower for American Indian and Alaska Native women,” said Emerson. “It’s likely rates are even lower for American Indian and Alaska Native women who live in rural areas or on tribal lands and who face even more economic and social obstacles—from health insurance coverage to internet access to transportation—when seeking breast cancer care.”

Emerson said he hopes the findings will help doctors who see American Indian and Alaska Native patients. “Knowing that these women have lower rates of use may help clinicians discuss the importance of starting and adhering to these medications or encourage them to tell their patients to contact them if they are having side effects, can’t afford the medication, or intend to stop taking it.”

Authors and Disclosures

This research was supported by the National Cancer Institute.

Co-authors include Ninah S. Achacoso, MS, of the Division of Research, and Halei C. Benefield, PhD, and Melissa A. Troester, PhD, of UNC Lineberger and UNC Gillings School of Global Public Health.

—Sue Rochman, Kaiser Permanente Northern California Division of Research