There are scientific suggestions that weight loss medications, such as semaglutide and tirzepatide, may help reduce the risk of developing certain types of cancer or benefit patients; however, more evidence is required for definitive conclusions.
Mechanism of Action and Research
In addition to established benefits in combating obesity and type 2 diabetes, GLP-1 agonists, known as 'weight loss injections,' may be associated with a reduced risk of progression of certain types of malignant tumors. New studies point to possible positive effects, particularly concerning breast, intestinal, lung, and liver cancer.
Obesity is recognized as a risk factor for many types of cancer. For instance, weight loss after bariatric surgery has already demonstrated a positive impact on disease prevention. With the proliferation of GLP-1 agonists, a gut hormone involved in regulating glucose levels and satiety, researchers have begun to investigate whether similar advantages can be observed with these injections. These drugs are prescribed for the treatment of type 2 diabetes and obesity because they help control blood sugar, reduce appetite, and promote weight loss.
Biological Rationale
Internist Diego Toledo from Einstein Hospital Israelita notes: 'Cancer is a metabolic disease. When we improve this metabolic environment and reduce inflammation associated with obesity [with medication], there is a consistent biological rationale for studying the impact on oncology.'
The possibility of such drugs, like semaglutide and tirzepatide, influencing cancer risk is not entirely new. In 2024, a study published in JAMA Network Open among over 1.6 million people with type 2 diabetes found a correlation between the use of GLP-1 agonists and a lower likelihood of developing some of the 13 types of cancer associated with obesity.
Results of Large Clinical Analysis
One of the most significant presentations at the annual American Society of Clinical Oncology (ASCO) meeting, held from May 29 to June 2 in the United States this year, advanced this discussion. It investigated whether these medications could influence disease development in patients who already have a diagnosis. The analysis covered data from 12,112 patients with seven types of tumors associated with obesity (breast, prostate, lung, colorectal, liver, kidney, and pancreas) in early or locally advanced stages, meaning confined to the organ but with a risk of metastasis.
In this study, scientists compared patients taking GLP-1 agonists with those receiving other diabetes medications to understand if using these drugs could reduce the risk of the disease progressing to a metastatic form. The results showed that in four out of the seven types of cancer studied, patients using GLP-1 agonists had a lower risk of developing metastases.
Specific data shows: for lung cancer, 10% of users of these medications developed metastatic disease compared to 22% among those treated with other diabetes drugs. For breast cancer, the percentages were 10% and 20%, respectively. For colorectal cancer—13% versus 22%. Regarding liver tumors, progression occurred in 19% of GLP-1 agonist users compared to 28% in the control group. In fact, this provided a reduction in the risk of progression to metastatic disease by 38%–50% in these four types of cancer.
Limitations and Differences
However, it cannot be claimed that the benefit is due to the direct action of these drugs on tumors, or that it is a consequence of indirect weight loss, reduced inflammation, and improved metabolism. Toledo emphasizes: 'Despite the lack of more convincing evidence of benefit, it is significant to observe a lower risk of developing more advanced forms of the disease in some types of cancer.'
It is known that adipose tissue functions not only as an energy reserve—it also produces substances capable of influencing various biological processes, including mechanisms related to tumor development. Therefore, reducing excess fat may bring benefits beyond simple weight loss.
According to studies analyzing the effect of GLP-1 agonists against cancer, the results are not uniform across all tumor types. Among urological tumors, particularly prostate and kidney, no benefit was observed. Andre Paterno, a clinical oncologist at Einstein and a specialist in the diagnosis and treatment of urogenital tumors, states: 'Although no significant reduction was noted, this does not mean that using the drug in this population carries any harm. Nor can potential benefit be ruled out.'
One possible reason lies in the biological nature of the disease itself. Prostate cancer often exhibits slower development, strong hormonal influence, and greater heterogeneity among patients. Paterno notes: 'There are many factors influencing its development, such as age, hormones, and the treatment patients received during the study.'
Another possibility relates to sample size. Although the study included thousands of participants, the number of participants decreases significantly when researchers analyze a specific tumor type. The differences between tumors suggest that the specific biological factors of each disease may influence the response to these medications, explaining the unevenness of the results.
Need for Further Research
Currently, the results do not allow the conclusion that weight loss drugs are responsible for reducing the risk of cancer progression. The main limitation lies in the research methodologies. Instead of selecting patients and tracking them over a long period in specially designed prospective studies, many works analyzed already registered information in medical databases, which is called retrospective research. Such analysis is useful for generating hypotheses, but it provides less guarantee for establishing causality.
In such cases, it is harder to separate the drug's effect from other patient characteristics that might influence the results, such as differences in medical monitoring, control of other diseases, lifestyle, and even access to healthcare. The oncologist explains: 'Patients using these medications typically have more frequent medical monitoring and often undergo other health changes. All of this can influence and must be considered when interpreting the results.'
Furthermore, studies have not yet been designed to address important clinical questions, such as the effect of these medications on patients undergoing chemotherapy, immunotherapy, or hormone therapy. Paterno concludes: 'The question of these drugs and cancer is a new frontier of research, but it does not yet represent a new clinical practice. This data generates important hypotheses, but they are not conclusive.'
To confirm that the observed benefit is truly linked to the use of these medications and to determine which patients might benefit from them, more robust analyses are needed, involving prospective patient observation and their random assignment to treatment groups. Paterno insists: 'No one should start [using] semaglutide, tirzepatide, or any other 'injection' to prevent or treat cancer. The official indication today remains obesity and type 2 diabetes, and always under the supervision of a specialized physician.'
Importance of Muscle Mass
The general consensus among specialists concerns body composition. More important than just weight loss is understanding what is being lost. In cancer patients, this distinction can affect the response to treatment and quality of life. The internist advises: 'Reducing fat mass while preserving muscle mass is among the factors associated with better outcomes in obese and cancer patients. Therefore, body composition deserves as much attention as weight.'
The focus should be not only on reducing fat tissue but also on preserving muscle mass, which affects functional capacity, treatment response, and recovery. This concern is especially relevant since many oncological patients already face weight loss, fatigue, appetite changes, and inflammation associated with the disease or treatment itself.
When weight loss occurs too rapidly and is accompanied by a decrease in muscle mass, the consequences can be detrimental, even in obese individuals. The oncologist warns: 'Excessive weight loss and, especially, muscle mass loss can lead to cachexia, a condition associated with poorer oncological outcomes.'
Therefore, it is crucial that any use of these medications in cancer patients be done individually and within a broader care approach that includes adequate nutrition, physical activity, and body composition monitoring.