A study published in the Journal of the National Comprehensive Cancer Network found that obesity at baseline is a poor prognostic factor for women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer; however, a 5% weight loss during treatment and follow-up also negatively impacted clinical outcomes. Weight gain did not appear to affect outcomes in these patients.
The randomized, phase III ALTTO BIG 2-06 trial included 8,381 patients with HER2+ early breast cancer who were treated with chemotherapy plus trastuzumab and/or lapatinib. Body mass index (BMI) was analyzed at randomization and two years later using World Health Organization BMI categories to classify patients as: underweight, <18.5 kg/m2 (n=187; 2.2%); normal weight, 18.5 kg/m2 to 24 kg/m2 (n=3,797; 45.3%); overweight, ≥25 to 29 kg/m2 (n=2,690; 32.1%); and obese ≥30 kg/m2 (n=1,707; 20.4%). Weight change from baseline of ≥5% was categorized as weight gain, and weight change ≤5% was categorized as weight loss.
Most patients were white (69%), and median follow-up was 4.5 years (range, 3.6-5.0 years). Obese patients were more likely to come from Europe (P<0.001), be white (P<0.001), be younger (<65 years; P<0.001), be postmenopausal (P<0.001), and have tumors 3 cm to 5 cm (P<0.001) that are more often poorly differentiated (P<0.001).
Compared with normal weight, obesity at randomization was associated with significantly worse distant disease-free survival (DDFS; adjusted hazard ratio [aHR], 1.25; 95% confidence interval [CI], 1.04-1.50) and overall survival (OS; aHR, 1.27; 95% CI, 1.01-1.60). However, researchers observed no significant difference in in disease-free survival (DFS; aHR, 1.14; 95% CI, 0.97-1.32).
Weight loss ≥5% two years after randomization was associated with significantly poorer DFS (aHR, 1.34; 95% CI, 1.05-1.71), DDFS (aHR, 1.46; 95% CI, 1.07-1.98), and OS (aHR, 1.83; 95% CI, 1.18-2.84). Hormone receptor and menopausal status influenced outcomes, while anti-HER2 treatment type did not. Obese patients more commonly experienced grade 3/4 adverse events (AEs), one or more serious AEs, and treatment discontinuation.
“Dietary counseling should be part of survivorship care programs,” the researchers commented.