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A weight-loss program delivered mostly over the phone improved physical function, social function, and mental health in women with overweight or obesity and early breast cancer, according to a substudy of a phase 3 trial.

At 6 months, women who received coaching reported better outcomes than control individuals across multiple measures, including physical function, physical health, mental health, and social functioning, while also reporting less fatigue. Improvements in all domains except fatigue persisted at 2 years.

The telephone-based weight-loss intervention “was successful in inducing durable improvements,” said lead investigator Jennifer Ligibel, MD, while presenting the findings at a preconference press briefing for the American Society of Clinical Oncology (ASCO) 2026.

The findings come from the BWEL trial. The primary objective is to see if weight loss improves invasive disease-free survival, given the link between higher BMI and worse breast cancer outcomes. The trial has enrolled over 3000 women with stage II/III HER2-negative breast cancer and a BMI of at least 27 from more than 600 oncology practices in the US and Canada.

The new analysis included the first 540 women enrolled in BWEL. All participants received educational materials about the benefits of weight loss and exercise, but half were also randomly assigned to a telephone coach to help hit calorie and physical activity goals.

Investigators previously reported that women in the coaching arm lost significantly more weight than control individuals at 1 year. Now it looks like they also felt better, based on PROMIS-29 Profile 2.0 and Global Health scores.

Half a year in, women who were coached scored an average of 1.9 points higher than control individuals on physical function, 2 points higher on physical health, 1.3 points higher on overall mental health, and 2.3 points higher on social functioning. They also scored 1.7 points lower on fatigue. With the exception of fatigue, the benefits persisted at 2 years.

The gains, however, were modest. A 2-point difference in the trial is at the threshold of clinical relevance, and the intervention did not improve anxiety, depression, sleep, or pain interference with daily activities, said Ligibel, who is a medical breast oncologist at the Dana-Farber Cancer Institute in Boston.

She explained that larger benefits are showing up in women who struggle more with physical function and mental health at baseline than other patients.

BWEL Details

The intervention in BWEL lasts 2 years. The educational materials participants receive are from the National Cancer Institute, backed up by quarterly newsletters and twice-yearly webinars.

Women randomly assigned to the intervention arm are paired with a coach at Dana-Farber who helps them meet calorie, weight, and physical activity goals.

Coaching calls are weekly for the first 3 months, then every 2 weeks through year 1 and monthly in year 2. Weights are measured in the clinic, physical activity is tracked with Fitbits, and the data are recorded in a web portal.

Study discussant Julie Gralow, MD, said the field is eagerly awaiting the primary results of BWEL, but in the meantime, the quality-of-life benefits of weight loss “are undeniable.”

BWEL “is challenging us to stop viewing lifestyle interventions as just optional add-ons and start integrating them as standard components of a comprehensive survivorship care plan. We need to advocate for resources, insurance reimbursements, and accessible programs” to make it happen, said Gralow, breast medical oncologist at the University of Washington in Seattle.

“We need these programs to become a part of standard care,” Ligibel added, because “it’s hard to do this on your own.”

Gralow said the success of the telephone-based approach “proves we don’t necessarily need patients to come into a specialized clinic every week to achieve significant lifestyle changes.”

GLP-1 agonists aren’t part of BWEL, but Ligibel said the weight-loss drugs may have a role in breast cancer.

Although exercise and good nutrition have benefits beyond weight loss, whether they deliver enough weight loss to improve breast cancer outcomes won’t be known until BWEL reports its primary results.

The study was funded by the National Cancer Institute, the Susan G. Komen Foundation, the Breast Cancer Research Foundation, and the American Cancer Society.

Ligibel reported having no disclosures. Gralow reported serving as an advisor for AstraZeneca, Genentech, Immunomedics, and Sandoz.

M. Alexander Otto is a physician assistant and award-winning journalist. He is also an MIT science journalism fellow. Email: aotto@medscape.net