Kaiser Permanente Study Finds Least Aggressive Form of Breast Cancer Still Poses Risk for Death Years Later

Findings could affect how doctors treat the most common breast cancer

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Sep 18, 2012, 01:46 ET

PASADENA, Calif., Sept. 18, 2012 /PRNewswire/ -- Women with the most common and least aggressive subtype of breast cancer were still at risk of death from the disease more than 10 years after diagnosis, according to a Kaiser Permanente study published in the journal Cancer Epidemiology, Biomarkers & Prevention.

The 21-year study included nearly 1,000 women from Kaiser Permanente Southern California and found that molecular subtypes of breast cancer were important independent predictors of breast cancer mortality. In particular, women with luminal A tumors — a subtype of breast cancer that is generally thought to have the best prognosis — were still at risk for death from the cancer more than 10 years after diagnosis.

Researchers also found that women with HER2-enriched and luminal B tumors had roughly a two-fold increased risk of death from breast cancer compared to women who are diagnosed with luminal A tumors, a finding that is consistent with previous studies.

"The findings of this study indicate that it is important to consider breast cancer molecular subtypes in determining the optimal treatment for women with breast cancer," said study lead author Reina Haque, PhD, MPH, from Kaiser Permanente Southern California's Department of Research & Evaluation. "Women with luminal A tumors — the least aggressive but most common cancerous breast tumor — could benefit from extended treatment to improve their chances for long-term survival."

Breast cancer tumors are often divided into four molecular subtypes:

luminal A, which tends to have the best prognosis with fairly high survival rates;
luminal B, which typically occurs in younger women and has a poor prognosis;
the basal-like subtype, which also tends to occur in younger women, as well as African American women, and has a poor prognosis;
and the HER2-enriched subtype, which has a fairly poor prognosis and is prone to early and frequent recurrence and metastases.

Of the four subtypes, luminal A is the most common and is responsible for 42 percent to 59 percent of all breast cancer cases.

Breast cancer is the second-leading cause of cancer death in women and will be responsible for nearly 40,000 deaths among U.S. women this year, according to the American Cancer Society. The risks for developing breast cancer increase as a woman ages, while other factors include genetics, personal health history and diet.

"These and earlier findings strongly support molecular subtypes as important independent predictors of breast cancer mortality," said Haque. "It is important for women with breast cancer, even those diagnosed with the least aggressive form of the disease, to be an advocate for their own health and speak to their doctors about treatment options."

Researchers suggest that future breast cancer studies should focus on identifying factors that are associated with longer survival in women with luminal A tumors as well as how the association between breast cancer molecular subtypes and survival varies by race and ethnicity, particularly in minority women who are more likely to have aggressive tumor subtypes.

This study is the latest Kaiser Permanente research effort to understand the effects of breast cancer. In January, Kaiser Permanente Colorado Institute for Health Research contributed to new research that reveals substantial differences — by both surgeon and institution — in the rates of follow-up surgeries for women who underwent a partial mastectomy for treatment of breast cancer. The differences, which cannot be explained by a patient's medical or treatment history, could affect both cancer recurrence and overall survival rates, according to the study.

And last year, research scientists at the Kaiser Permanente Northern California Division of Research found that breast cancer survivors who experience significant weight gain have an increased risk of death after diagnosis and were 14 percent more likely to experience a cancer recurrence compared to women whose weight remained stable following diagnosis.

The original study was funded through the California Breast Cancer Research Program. Additional work was supported by the National Institutes of Health/National Cancer Institute (R01CA136743-01) and the Breast Cancer Research Foundation.

Other study authors included Syed A. Ahmed, MD, Galina Inzhakova, MPH, Jiaxiao Shi, PhD, Chantal Avila, MA, Shelley M. Enger, PhD, and Jonathan Polikoff, MD — all from the Kaiser Permanente Southern California Department of Research & Evaluation; Leslie Bernstein, PhD, of the City of Hope Department of Population Sciences; and Michael F. Press, MD, PhD, of the University of Southern California Norris Comprehensive Cancer Center.

About the Kaiser Permanente Southern California Department of Research & Evaluation
The Department of Research & Evaluation (R & E) conducts high-quality, innovative research into disease etiology, prevention, treatment and care delivery. Investigators conduct epidemiology, health sciences, and behavioral research as well as clinical trials. Areas of interest include diabetes and obesity, cancer, HIV/AIDS, cardiovascular disease, aging and cognition, pregnancy outcomes, women's and children's health, quality and safety, and pharmacoepidemiology. Located in Pasadena, Calif., the department focuses on translating research to practice quickly to benefit the health and lives of Kaiser Permanente Southern California members and the general population. Visit www.kp.org/research.

About Kaiser Permanente
Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America's leading health care providers and not-for-profit health plans. Founded in 1945, our mission is to provide high-quality, affordable health care services to improve the health of our members and the communities we serve. We currently serve more than 9 million members in nine states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to www.kp.org/newscenter.

For more information:
Vincent Staupe, [email protected], 415.318.4386
Sandra Hernandez-Millett, [email protected], 626.405.5384

SOURCE Kaiser Permanente