GLP-1s: Weight Loss and Survival in Breast Cancer Recovery

For more than 20 years, Dana Brantley-Sieders viewed breast cancer through the controlled lens of a laboratory, studying the disease as a biomedical researcher. But in 2018, Brantley-Sieders, who holds a PhD, was diagnosed with the very disease she spent her career investigating. Two years later, the cancer recurred.

Following her treatment, Brantley-Sieders faced issues common to many survivors: profound fatigue and significant weight gain. Despite her professional knowledge of the molecular mechanics of the disease, she found that standard lifestyle interventions were no match for the metabolic shifts triggered by endocrine therapy. In an interview with CURE, she described the frustration of hitting a plateau where "society and all the messages that we get say you just have to have willpower [to lose weight]," yet her body refused to respond. At her heaviest, she weighed 226 pounds.

For Brantley-Sieders, now 53, living in North Carolina and working as part of the Susan G. Komen research team, her trajectory changed a year ago when she was prescribed a GLP-1 medication for diabetes. The results were transformative, not just for her weight — which dropped to between 176 and 180 pounds — but for her systemic health. Her hemoglobin A1c levels improved, her cholesterol stabilized, and even the liver toxicity she experienced from tamoxifen treatments began to resolve.

"It was life-changing," Brantley-Sieders says, noting a reduction in the "food noise" that often faces those facing challenges with their metabolic health. "I got to a point where I wanted to work out. I wanted to eat healthy... I felt so much better in my body."

The mechanics of a ‘game-changer’

The class of drugs Brantley-Sieders utilized — glucagon-like peptide-1 (GLP-1) receptor agonists — has rapidly moved from the periphery of diabetes management to the center of oncology research.

Dr. Sonja Hughes, vice president of community health at Susan G. Komen, explained that GLP-1s are medications that mimic a hormone naturally produced in the human gut. "That glucagon-like peptide normally controls blood sugar, curbs appetite and slows down digestion," Hughes says. By regulating blood sugar and increasing feelings of fullness, these medications, which include brand names such as Ozempic, Wegovy and Zepbound, facilitate significant weight loss.

While originally developed for patients with type 2 diabetes, the medications’ secondary effects have opened new doors for cancer survivors. Hughes noted that while the medical community is currently navigating a "massive surge in data," it is vital for patients to separate clinical promise from media hype. "The most important thing has not changed," she cautions. "Discuss your specific condition and your specific risk with your healthcare provider."

Breaking the cycle of fatigue

For Lori McLean, the struggle wasn’t just with the scale; it was with a crushing exhaustion that lasted for years. Diagnosed with stage 2 breast cancer in 2017, McLean underwent a mastectomy and radiation before beginning a seven-year regimen of tamoxifen.

"The part I struggled with the most is fatigue," McLean recalls. "Finally, at seven years I said to my oncologist, 'I just can't do this anymore.'" By the time McLean finished her hormone therapy, she had gained 50 pounds. "I feel like everything I ate went in my mouth and then on my hips."

In 2024, at the suggestion of her endocrinologist, McLean started a GLP-1 medication. Now 56 and living in North Carolina, she has since lost the 50 pounds she gained during treatment. Beyond the physical change, she reports a fundamental shift in her relationship with food and her overall vitality.

"Mentally, it's a great feeling when you can open your closet, and you can go, 'I can put on any pair of pants I want,'" McLean says. Now a leader for the Komen Triangle Race for the Cure, she uses her platform to tell other survivors they aren't alone in the metabolic struggle that often follows cancer. "My goal is to talk about it so people realize they're not alone in the journey."

ASCO 2026: Evidence of a survival benefit

The anecdotal success of patients such as Brantley-Sieders and McLean is now being backed by massive real-world data sets, many of which were the highlights of the American Society of Clinical Oncology (ASCO) 2026 Annual Meeting.

A landmark retrospective analysis from Penn Medicine, involving more than 110,000 women, found that those taking GLP-1 medications were approximately 30% less likely to develop breast cancer than those who did not. "While our study was observational ... it does add to the growing body of evidence suggesting that it’s worth investigating these weight-loss drugs as potential cancer prevention tools," said Dr. Elizabeth McDonald, a professor of Radiology at the University of Pennsylvania, in a news release detailing the data.

Further studies presented at ASCO 2026 signaled even broader benefits, as follows:

• Research from Harvard University and Ontada observed an almost 35% reduction in the rate of death among GLP-1 users across six different solid tumor types.
• The Cleveland Clinic reported a 34% mortality reduction in obesity-related solid tumors, suggesting that high GLP-1 receptor expression might even act as a direct antitumor signal.
• The largest study of its kind, with researchers from The University of Texas MD Anderson Cancer Center evaluating over 1,000 breast cancer survivors, confirmed that GLP-1 use was associated with improved all-cause survival. However, this specific study did not find a significant difference in the risk of breast cancer recurrence, suggesting that the survival benefit may stem from improved cardiovascular and metabolic health.

A call for caution in timing

Despite the optimism, experts emphasize that GLP-1s are not a universal "magic pill" for every stage of the cancer journey. Dr. Neil M. Iyengar, an associate professor at the Emory University School of Medicine and director of Survivorship Services at the Winship Cancer Institute, urges caution regarding the timing of these medications.

"We don’t have robust data regarding the safety of these drugs during active cancer therapy, like chemotherapy," Iyengar says. He raised two primary concerns: the potential for GLP-1s to cause a loss of lean muscle mass — which is vital for insulin metabolism during treatment — and preliminary data suggesting the drugs could alter immune cells in a way that might interfere with immunotherapy.

For survivors already on long-term endocrine therapy, Iyengar noted that the weight loss effects of GLP-1s might actually be attenuated. Observational data suggest that survivors on hormone therapy may lose less than 5% of their body weight, compared with the 10%-15% seen in the general population.

"Something about the interaction between the GLP-1 and the hormone therapy is making the GLP-1 receptor agonist less effective for weight loss," Iyengar explains, noting that increasing the dose is often limited by side effects such as nausea.

Why is weight loss so uniquely difficult for breast cancer survivors? Dr. Sriram Machineni, director of the Fleischer Institute Medical Weight Center at Montefiore Einstein — home to NCI-designated comprehensive cancer center, Montefiore Einstein Comprehensive Cancer Center — said the answer lies in the neuroendocrine disruption caused by cancer treatments.

Treatments such as tamoxifen and Lupron (leuprolide) work by depriving the body of estrogen, which is essential for the tumor's growth but also critical for the brain's sensitivity to leptin, the hormone that signals fullness.

"By depriving estrogen, we are also taking away some of the other things that estrogen is really important in," Machineni says. This creates a "perfect storm": Survivors feel hungrier, their bodies burn energy less effectively and they suffer from fatigue that limits their ability to exercise.

"Despite a person having really good commitment to exercise and eating right, their biology is constantly fighting them at every turn," Machineni notes.

GLP-1s succeed where lifestyle changes fail because they bypass these disrupted estrogen pathways to directly activate satiety signals in the brain. Furthermore, Machineni pointed to the drugs’ ability to reduce the activation of inflammatory cells in the brain, which may explain the profound reduction in systemic fatigue reported by patients.

The realities and trade-offs of success

For Dina Lorraine, a four-time cancer survivor and patient at Fred Hutch Cancer Center, the decision to start Zepbound in 2025 was a "no-brainer." Over years of chemotherapy and steroid use for thyroid cancer, melanoma, lobular breast cancer, and peritoneal carcinoma, Lorraine, now 58 and living in Washington, had gained 60 pounds. The weight was so significant that her implanted sleep apnea device was no longer effective, leaving her feeling like she was being "electrocuted" at night as she struggled to breathe.

"You already feel ugly — you've lost your breasts, you have no hair," Lorraine said. "Then on top of it, you're overweight, and you feel like you're not even in your own body anymore."

Lorraine lost 70 pounds in nine months, a result she calls a "game-changer" for her energy and sleep apnea. However, the achievement came with stark trade-offs. She experienced hair loss and gastrointestinal issues, and the rapid weight loss left her reconstructed breasts looking like "skin bags."

"I went from having a body after the DIEP flap surgery that I could go and not wear a bra at all...to now needing to wear an underwire bra," Lorraine shares. Despite needing revision surgery, she remains steadfast in her choice. "I look so much better than when I had the weight that it’s a trade-off I’m willing to take."

Looking toward a thriving future

As researchers look to the future, the goal is shifting from surviving cancer to thriving in the decades that follow.

For Brantley-Sieders, her personal journey has deeply informed her professional work with Susan G. Komen. She is now a vocal advocate for ensuring that these medications are covered by insurance as a medical necessity, rather than being dismissed as a "vanity thing." "This is really about health," she said.

The potential for GLP-1s to mitigate the risk of recurrence — particularly for hormone receptor-positive cancers that can return decades later — remains the most critical frontier for research. While the MD Anderson study showed improved survival but not necessarily a lower risk of recurrence, the medical community is eager for the results of upcoming prospective clinical trials.

Hughes emphasizes that as these "precise treatments" become more common, the focus must also turn toward health equity. "Everyone has the right and a fair chance of access to care," she said, noting that Black women are 40% more likely to die of breast cancer. Ensuring that these potentially life-changing drugs reach underserved communities is essential to closing the survival gap.

For Brantley-Sieders, the intersection of her research and her reality provided a new perspective on survivorship. "I know we're so focused on 'we're going to beat this cancer,' but just in terms of life goes on, what can we do to make sure you're not just surviving, but you're thriving?"