Metformin has been used for decades to help people manage type 2 diabetes, but scientists are increasingly interested in benefits that may go beyond blood sugar control.
A recent study suggests that people taking the medicine may have a lower risk of developing the two most common types of skin cancer.
The findings add to growing research on metformin’s possible effects on cancer.
Skin cancer is extremely common, especially in countries where people receive high levels of sun exposure. Basal cell carcinoma, or BCC, and squamous cell carcinoma, or SCC, are known as non-melanoma skin cancers. They are usually less deadly than melanoma, but they can still damage surrounding tissue and sometimes require extensive treatment.
BCC begins in cells near the bottom of the skin’s outer layer and makes up most non-melanoma skin cancers. SCC develops in another type of skin cell and can sometimes grow more aggressively or spread to other parts of the body. Exposure to ultraviolet radiation from sunlight is a major risk factor for both cancers.
Researchers led by Dr. Tiffany Libby, an assistant professor of dermatology at Brown University, examined whether metformin use was associated with the likelihood of developing these cancers. They used information from a large and diverse health database supported by the U.S. National Institutes of Health. This allowed the team to compare thousands of people with and without skin cancer.
The analysis included more than 8,000 people diagnosed with basal cell carcinoma and over 4,100 with squamous cell carcinoma. Each person with cancer was compared with four people without the disease who were matched by factors including age, sex, race, and ethnicity. The researchers also considered the possible effects of other medicines.
The results showed that people who used metformin had a significantly lower likelihood of developing either BCC or SCC. This relationship remained after the researchers adjusted their analysis for other medications that might influence cancer risk. The findings do not prove that metformin directly prevents skin cancer, but they suggest a possible protective connection.
One important difference appeared among Black patients. Metformin use was not linked to a lower risk of squamous cell carcinoma in this group. The researchers suggested that this could be related to differences in how SCC develops in people with darker skin.
In Black patients, squamous cell cancers are more likely to appear in areas that receive little sun exposure and may sometimes develop in skin affected by long-term inflammation, wounds, or scars. If these cancers develop through different biological pathways, metformin may not have the same protective effect. More research involving diverse populations will be needed to understand this finding.
Scientists have several ideas about how metformin might influence cancer. Laboratory research suggests that the medicine can interfere with processes cancer cells use to obtain energy and grow. It may also affect inflammation, immune responses, and the development of blood vessels that tumors need to receive oxygen and nutrients.
Metformin is inexpensive, widely available, and generally well understood because it has been prescribed for many years. However, that does not mean people without diabetes should begin taking it to prevent skin cancer. The new findings come from an observational analysis, and clinical trials would be needed to determine whether the medicine can safely and effectively prevent these cancers.
Standard skin cancer prevention remains important regardless of medication use. Limiting excessive ultraviolet exposure, using sun protection, and having suspicious or changing skin spots checked by a healthcare professional can help reduce risk or detect cancer earlier. People taking metformin should continue using it according to their doctor’s instructions rather than changing treatment because of these findings.
The study was led by Dr. Tiffany Libby and colleagues at Brown University and was published in the Journal of Drugs in Dermatology. The results support further investigation into whether a familiar diabetes medicine could eventually play a role in preventing some of the world’s most common cancers.
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