Data shows association between increased weight and breast cancer survival varies by race/ethnicity

An extreme body mass index or high waist-to-hip ratio, both measures of body fat, increased risk for mortality among patients with breast cancer, but this association varied by race/ethnicity, according to recently presented data.

Marilyn L. Kwan, Ph.D., a research scientist in the Kaiser Permanente Northern California Division of Research in Oakland, Calif., presented these results at the Fifth AACR Conference on The Science of Cancer Health Disparities, held here Oct. 27-30, 2012.

Prior research has shown racial/ethnic differences in survival after a breast cancer diagnosis, particularly among non-Latina whites and African-Americans, according to Kwan. However, reasons for these differences in survival are not clear, and researchers have hypothesized that body size at the time of breast cancer diagnosis might play a role.

"The majority of studies among primarily non-Latina white populations on obesity before a diagnosis of breast cancer have found that increased weight is associated with poorer survival, yet few studies have examined if this association holds true within the major minority groups of African-Americans, Latinas and Asians and whether differences in obesity might explain racial/ethnic differences in survival," Kwan said.

She and her colleagues collected data from 12,025 female patients with breast cancer from the California Breast Cancer Survivorship Consortium. Body mass index (BMI) information was available for 11,351 women including 6,044 non-Latina whites, 1,886 African-Americans, 1,451 Asian-Americans, 1,864 Latinas and 106 others.

"Overall, we found that patients with breast cancer who were underweight, extremely obese or had high levels of abdominal body fat had the worst survival," Kwan said.

In fact, those women classified as underweight had a 47 percent increased risk for overall mortality compared with normal-weight women. Women classified as morbidly obese had a 43 percent increased risk for overall mortality. In addition, women with the highest waist-to-hip ratio (highest level of abdominal fat) had a 30 percent increased risk for overall mortality and a 36 percent increased risk for breast cancer mortality compared with those with the smallest waist-to-hip ratios.

When looking further at mortality within racial/ethnic groups, the researchers found that associations differed by race/ethnicity.

"Among non-Latina white women, being underweight and morbidly obese at breast cancer diagnosis was associated with worse survival, yet this relationship was not found in the other racial/ethnic groups," Kwan said. "Instead, African-American women and Asian-American women with larger waist-to-hip ratios had poorer survival, an observation not seen in non-Latina white women and Latina women."

Latina women had an elevated risk for mortality only among those considered morbidly obese. According to Kwan, this study supports the common lifestyle recommendation to maintain a healthy weight throughout life, but she pointed out that the long-term impact of weight on survival after breast cancer might not be the same in all patients.