Wow. A super interesting study just came out looking at GLP effect on breast cancer. For those of you who want to cut to the summary, it showed GLP use lowered breast cancer rates. Please read my summary of thoughts at the end.
This was a study out of UPenn which looked at 111,000 women to see if GLP use affected breast cancer rates. They start by stating “excess weight is a key modifiable risk factor for breast cancer.” Their study recently published in June 2026 (yes, this is hot off the presses) “GLP 1 Agonists Are Associated with Significant Reduction in Breast Cancer Incidence in Women.”
Study:
Findings?
It is unclear if this is due to weight loss as the women had a BMI of 25 or more (which has also been shown weight loss to lower breast cancer rates) or something inherent to the GLP. (See a study I blogged about in 2019 which showed a linear reduction in breast cancer risk with weight loss BREAST CANCER WEIGHT). Other studies have shown Metformin and Losing Weight lower breast cancer incidence
In 2019, I blogged about this on my website. “Sustained Weight Loss and Risk of Breast Cancer in Women 50 Years and Older: A Pooled Analysis of Prospective Data.”
Study:
There were multiple studies which came out which indicated metformin use helped reduce breast cancer occurrence. Just to cite two:
Metformin and breast cancer incidence in postmenopausal diabetic women in the Women’s Health Initiative (WHI) came out in 2011. Remember, this was done on postmenopausal diabetic women.
They conclude, “In diabetic women… this proves support for testing metformin in chemoprevention.”
I believe in this. IF your weight is higher (BMI >25), you are prediabetic (HbA1c 5.6 or higher), or are diabetic, all of these studies reinforce that 1. losing weight and 2. being on medications which fight prediabetes and diabetes (GLP and metformin) have lower rates of breast cancer.
It is unclear if there is a benefit to those who are NOT overweight or are NOT prediabetic. This is not a mandate for all women to be on GLP medications. But it is reinforcement for people who are a little overweight, particularly for menopausal women, to lose the weight. It is reinforcement to those who are prediabetic to try to fight that- lose weight, build muscle, watch what you eat, walk after meals, limit carbs, do a continuous glucose monitor. We may find there is a value of GLPs to women who do not fit these categories, but as of now, there is no evidence.
I will continue to update as more studies come out. For the medical references, please read below. You will see many studies are recent. This is evolving.
Survival and Recurrence With GLP-1 Receptor Agonists in Breast Cancer, JAMA, May 2026
Sustained Weight Loss and Risk of Breast Cancer in Women 50 Years and Older: A Pooled Analysis of Prospective Data, Journal of National Cancer Institute, 2019
Metformin and Incident Breast Cancer among Diabetic Women: A Population-Based Case–Control Study in Denmark, Cancer Epidemiology Biomarkers and Prevention 2011
Metformin and breast cancer incidence in postmenopausal diabetic women in the Women’s Health Initiative (WHI)., Journal of Clinical Oncology 2011
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