Major Finding: Women with BMIs of 25–30 and greater than 30 were 26%–38% more likely than normal weight women to die of breast cancer 10 or more years after diagnosis.
Data Source: An analysis of a registry involving nearly 19,000 women with breast cancer.
Disclosures: Dr. Ewertz received a research grant from Novartis Pharmaceuticals Corp., and GlaxoSmithKline sponsored her trip to the meeting. The study, however, was conducted and analyzed without support from pharmaceutical companies.
SAN ANTONIO — Obese women are substantially more likely than women of normal weight to die of breast cancer, a large Danish registry study concluded.
Researchers from the Danish Breast Cancer Cooperative Group examined extensive health information from nearly 19,000 women with breast cancer, with follow-up data available for up to 30 years post diagnosis.
Breast cancer patients with body mass indexes (kg/m
The disparity showed up early in the course of their disease, Dr. Marianne Ewertz said at the annual meeting of the San Antonio Breast Cancer Symposium.
“For distant metastasis, the curves begin to separate after 3 years,” said Dr. Ewertz, professor of oncology at Odense (Denmark) University Hospital.
By 5 years, women with a BMI of 25–30 had an increased adjusted hazard ratio of developing distant metastasis of 1.42 (95% confidence interval, 1.17–1.73; P = .0005). For those with a BMI greater than 30, the adjusted odds of distant metastasis beginning at 5 years were 1.46 (95% confidence interval, 1.11–1.92; P = .007).
Women with BMIs of 25–30 and greater than 30, respectively, were 26%–38% (P = .002 and .003) more likely than normal-weight women to die of their disease 10 or more years after diagnosis, and more likely to die of other causes as well.
Heavier women in the study were older, were more likely to be postmenopausal, had larger tumors, had more positive lymph nodes, and had more tumor invasion into deep fascia than did those with a BMI less than 25 (all P values less than .0001). They also had more grade 3 tumors (P = 0.04).
However, all of these factors were statistically accounted for in the multivariate analyses of distant metastasis and overall survival.
Poorer outcomes over time may indicate that adjuvant therapy is less effective in obese women than in normal-weight women, Dr. Ewertz suggested.
Inadequate dosing or biological factors could account for the study's findings, said Dr. Michelle D. Holmes of the Dana-Farber/Harvard Cancer Center in Boston, who was the formal discussant of the presentation.
The impact of lifestyle factors on cancer can be “confounding” because they cannot be studied in prospective, randomized trials.
Therefore, prospective observational evidence is gathered from huge, well-controlled population databases such as the Danish health registries. “This is kind of as good as it gets, and it's pretty good,” Dr. Holmes said.