More study details
The findings come from the French National Epidemiological Strategy and Medical Economics–Metastatic Breast Cancer observational cohort, which includes 22,000-plus consecutive patients who were newly diagnosed with metastatic disease between 2008 and 2016.
A total of 12,999 women for whom BMI data were available when they were diagnosed with metastatic breast cancer were selected for analysis. They were divided into four groups, according to World Health Organization classification: underweight (BMI <18.5 kg/m2), normal weight (18.5-24.9), overweight (25.0-29.9), and obese (≥30.0).
A total of 20% of women were obese, which is a much lower percentage than the 40%-50% that would be expected in a comparable American cohort, said Dr. Ligibel. Also, 5% of the French cohort was underweight.
Multivariate Cox analyses were carried out for OS and for first-line progression-free survival (PFS).
As noted above, underweight was independently associated with a worse OS. It was also tied to worse first-line PFS (HR, 1.11; 95% CI, 1.01-1.22). Overweight or obesity had no effect.
“Patients with a low BMI had more visceral metastases and a greater number of metastatic sites,” pointed out study author Dr. Deluche. “We attribute the fat loss in patients with metastatic breast cancer to aggressive tumor behavior with a higher energy requirement.”
The study authors also observe that in early-stage breast cancer, underweight is not associated with overall or breast cancer–specific survival. “Underweight at metastatic diagnosis seems to have a different significance and impact,” they write. The French team also observes that, in other cancers, underweight is also an adverse prognostic factor and has been associated with a higher risk for death.
The study authors acknowledge that BMI has limitations as a measure of body type. “BMI alone cannot estimate a woman’s muscle mass and adiposity,” they observe. The suggestion is that, among women with a similar BMI, some might be muscular, whereas others might have more body fat.
Multiple study authors report financial ties to industry, including pharmaceutical companies with drugs used in breast cancer. The database used in the study receives financial support from AstraZeneca, Daiichi Sankyo, Eisai, MSD, Pfizer, and Roche. Dr. Ligibel reports no relevant financial relationships.
A version of this article first appeared on Medscape.com.