People with breast cancer with overweight or obesity can “improve their physical function and quality of life and reduce their symptoms,” according to a sub-study of the Phase III Breast Cancer Weight Loss (BWEL) clinical trial in which patients participated in a telephone-based weight-loss program. Findings were presented at the recent American Society of Clinical Oncology annual meeting (ASCO 2026) in Chicago.

 

The findings are significant, according to an ASCO perspective on the study, because “about one in eight women will be diagnosed with breast cancer in their lifetime” and “up to three in four people diagnosed with breast cancer are overweight or are obese.” What’s more, having excess body weight is a risk factor for breast cancer and is linked to increased side effects of cancer treatment.

 

“We’ve asked patients with Stage II to III breast cancer who are overweight or obese to lose weight for years without offering them much of a structured program. BWEL changes that conversation not just because of the survival data but also because patients in the intervention arm felt measurably better in their physical function, fatigue and social engagement. A program that improves survival and quality of life simultaneously is a program worth delivering,” said Marcin Chwistek, MD, chief of the Supportive Oncology and Palliative Care Program at Fox Chase Cancer Center, in an ASCO press release.

 

The study was led by Jennifer Ligibel, MD, director of the Leonard P. Zakim Center for Integrative Therapies and Healthy Living at the Dana-Farber Cancer Institute. 

 

As of January 2025, 18.6 million people are living with cancer or have a history of cancer, 4.5 million of whom have a history of breast cancer specifically. The American Cancer Society (ACS) projects that by 2035, over 22 million Americans will be cancer survivors, including 5.3 million breast cancer survivors.

 

According to the ACS, about 5% of cancers in men and 11% of cancers in women are linked to having excess body fat. For breast cancer, premenopausal women with overweight or obesity may have a slightly decreased risk for breast cancer; after menopause, they have an increased risk, according to Susan G. Komen. Fat cells make enzymes and hormones that can change estrogen and insulin levels and increase cancer risk. For the same reason, having overweight or obesity can complicate and increase symptoms associated with breast cancer treatment.

 

During the two-year BWEL trial—which involved diet, physical activity and behavioral changes—cancer patients were assigned a coach they could speak with on the phone up to 42 times to help them reach their goals. A Phase III clinical trial found that the BWEL program helped breast cancer patients reduce their caloric intake and increase physical activity.

 

A sub-study of the clinical trial followed 542 people undergoing breast cancer treatment for two years. Half of the participants were randomly assigned to participate in the BWEL program plus health education, which included a variety of materials emphasizing the importance of a healthy diet and regular physical activity, while the other half received only health education. Researchers evaluated physical, mental and social health scores at the six-month and two-year marks using the Patient-Reported Outcomes Measurement Information System (PROMIS), which rates scores on a 50-point scale.

 

Participants in the BWEL group had better physical function, with an average score 1.9 points higher than those in the health education group. Physical and mental health scores were on average 2 points and 1.3 points higher, respectively. BWEL participants also saw improvements in their ability to work and socialize, with average scores 2.3 points higher. They also had lower fatigue scores by an average of 1.7 points. All physical, mental and social improvements were also found at the two-year mark.

 

“The BWEL program was delivered to more than 1,500 participants enrolled from across 635 oncology practices in the U.S. and Canada. These findings thus show not only that weight loss provides meaningful benefits for people who have both breast cancer and obesity but also that this can be achieved in thousands of patients enrolled across many kinds of oncology practices,” said Ligibel.

 

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