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Obesity Impacts Breast Cancer Survival

Relationship strongest in ER positive breast cancers

May 25, 2011

Written By Janine E. Guglielmino, MA, Director, Programs and Strategic Initiatives
Reviewed By Kathryn Schmitz, PhD, MPH

An analysis of findings from several studies that followed women over long periods of time suggests an association between obesity at diagnosis and shorter overall survival among those with hormone receptor-positive breast cancer treated with chemotherapy.

The study, presented at the San Antonio Breast Cancer Symposium, looked at the relationship of obesity at diagnosis to survival within a variety of breast cancer subtypes. A statistically significant association was found only among women with estrogen receptor- or progesterone receptor-positive, HER2 negative disease. Changes in the chemical makeup of the body related to being obese, such as having too much circulating insulin, could explain survival differences, the researchers suggested.

Background and Goals of the Study

Many studies have found a relationship between obesity and survival in women with early-stage breast cancers. Some of these studies looked only at certain subtypes of breast cancer or included people who received different kinds of treatment.

In this study, the researchers looked at groups of women who received similar diagnoses and treatments. The goal was to measure the causal association between obesity and overall survival, the length of time participants lived after enrolling in the study, and disease-free survival, the length of time participants went without a recurrence of breast cancer after joining the study. A causal association looks for a relationship between factors in which a change in one creates a change in the other.

Structure of the Study

The researchers collected information from three previously conducted clinical trials, E1199, E5188 and E3189. Those trials asked a variety of questions, but all participants had stages I-III breast cancer and received post-surgical chemotherapy with doxorubicin (Adriamycin) and cyclophosphamide (Cytoxan) plus other medicines.

To search for a relationship between obesity and outcome, the researchers studied body mass index, a common measure of body fat in relation to a person’s height and weight. In the United States, a person with a BMI of 30 or more is considered obese. The participants’ BMI was compared to their disease-free and overall survival.

Also considered were breast cancer subtype, tumor size, cancer in the lymph nodes, ethnic background, type of surgery, previous radiation treatment status, menopausal status, treatment arm and whether the participant completed the recommended course of treatment.

Study Findings

When looked at as a group, obese participants in E1199 did slightly less well than non-obese participants. But when analyzed by breast cancer subtype, obese women with hormone positive, HER2 negative breast cancer had a significantly higher risk for death than non-obese women with the same breast cancer type. This relationship was not found in HER2 positive or triple-negative breast cancer.

To validate the findings, the researchers then looked at data from participants in E5188, who all had hormone positive disease, and women in the E3189 study, who all had hormone negative disease. The analysis confirmed the association between obesity at diagnosis and disease-free and overall survival only in the group of women with hormone positive breast cancer.

No significant associations were uncovered between obesity at diagnosis and the other factors studied.

What These Findings Mean for You

The analysis adds to the growing body of evidence that obesity at diagnosis is associated with a shortened lifespan for women with breast cancer. But to confirm the findings, researchers must conduct a prospective study to test tools that obese women could use to lose weight and maintain weight loss. By following these women through time, the researchers would see whether those tools affect outcome.

Future trials should also study whether excess insulin in the bloodstream, a common problem in obese people, encourages the growth of estrogen-sensitive breast cancers.

Although more research is needed, it’s always a good idea to maintain a healthy weight, eat nutritious food and regularly exercise. Doing so can help you feel your best, improve your mood and possibly protect you from a number of health problems. We know managing weight can be challenging, but you don’t have to go it alone. Talk with your healthcare team. We also invite you to read more on lbbc.org.

Sparano JA, Wang M, Martino S, Jones V, Perez EA, et al. Obesity at Diagnosis Is Associated with Inferior Outcomes in Hormone Receptor Positive Breast Cancer. Presented at: 33rd Annual San Antonio Breast Cancer Symposium; December 2010; San Antonio, TX.

Denver, CO  ·  September 13, 2014

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