A 5% weight loss over 2 years in patients with human epidermal growth factor receptor 2 (HER2)-positive early breast cancer was associated with worse outcomes, according to new research that investigated the body mass index (BMI) data of these patients.

"The finding that weight loss, and not weight gain, was associated with worse outcomes is unexpected," said lead researcher Samuel Martel, MD, Universitè de Sherbrooke, Quebec, Canada, in a press release. Martel worked with researchers based in Belgium, Brazil, Germany, Italy, Switzerland, and the United Kingdom, as well as the National Cancer Institute and the Mayo Clinic in the United States.

Martel noted that since they were unable to make a distinction between intentional versus unintentional weight loss, whether worse outcomes were due to weight loss or vice versa is speculative.

"We hope our findings highlight the importance of incorporating consecutive and prolonged data collection on weight in oncology trials, and gaining greater understanding of the metabolic processes after cancer diagnosis that may impact outcomes," Martel said in the press release.

The investigators collected height and weight data from 8381 patients with HER2-positive early breast cancer who were treated with chemotherapy plus trastuzumab and/or lapatinib during the ALTTO BIG 2-06 trial. Of the total patients, 2.2% were underweight at the beginning of the treatment period, 45.3% were at a normal weight, 32.1% were classified as being overweight, whereas 20.4% were classified as obese, meaning their BMI was greater than 30.

The investigators found that initial obesity was correlated with worse outcomes. These outcomes included more frequent and serious adverse events that caused treatment discontinuation, as well as significantly worse rates of overall survival.

"It was surprising to see that more than 5% weight loss at 2 years was associated with poorer distant disease-free survival,” said Anthony D. Elias, MD, University of Colorado Cancer Center, a member of the National Comprehensive Cancer Network Clinical Practice Guidelines Panel for Breast Cancer, in the press release.

Elias noted that these findings led him to question whether the general advice to obese and overweight patients to exercise and lose weight was wrong.

"Careful examination of the Kaplan-Meier hazard plots suggests that the relapse curves for those with weight loss are steeper in the second and third years of follow-up, but thereafter are relatively parallel. It's possible that the weight loss observed early may be an indication for impending relapse of breast cancer," Elias said in the press release.

Because of the questions raised by the study, the authors said that they hope their findings can act as the basis for further research and oncology trials that can provide more information for guiding weight control during the cancer survivorship period.

REFERENCE
Unexpected findings on weight loss and breast cancer from international study in JNCCN. Plymouth Meeting, PA: National Comprehensive Cancer Network; February 16, 2021. https://sciencesources.eurekalert.org/pub_releases/2021-02/nccn-ufo021621.php. Accessed February 17, 2021.