A number of studies have suggested a link between diabetes, diabetes medicines, and breast cancer risk. Research strongly suggests that women diagnosed with diabetes are more likely to be diagnosed with breast cancer than women who aren’t diabetic. Other research suggests that diabetic women taking the medicine metformin (brand names: Fortamet, Glucophage, Glumetza, Riomet), which is commonly used to treat type 2 diabetes, have a lower-than-average risk of breast cancer.
Now a small, early study suggests that women diagnosed with metastatic breast cancer who have insulin levels that are higher than normal, but aren’t diabetic, have a worse prognosis than women diagnosed with metastatic disease who have normal insulin levels.
The research was presented at the Advanced Breast Cancer Third International Consensus Conference on Nov. 6, 2015. Read the abstract of “Insulin Resistance (IR) and Prognosis of Metastatic Breast Cancer (MBC) Patients.” (PDF)
The hormone insulin helps our bodies regulate blood sugar (glucose). Insulin also helps cells grow. Many people who have diabetes and many obese people tend to have higher-than-normal insulin levels (hyperinsulinemia). This is partially because their bodies no longer respond to normal insulin levels. Some experts think that higher insulin levels may help breast cancer cells develop and grow.
This study involved 125 women diagnosed with metastatic, HER2-negative breast cancer. About 75% of the cancers were hormone-receptor-positive. None of the women had been diagnosed with diabetes. All the women were being treated with chemotherapy as part of clinical trial.
The women ranged in age from 36 to 86 years old. Most of the women were overweight or obese:
- 40.5% were overweight (BMI of 25-30)
- 16.37% were obese (BMI higher than 30)
The researchers looked at the relationship between how sensitive the women were to insulin and progression-free and overall survival.
Progression-free survival is how long the women lived without the cancer growing. Overall survival is how long the women lived, with or without the cancer growing.
People who are not sensitive to insulin are called “insulin-resistant.” In insulin-resistant people, the body has to make higher levels of insulin to keep blood sugar regulated. So people who are insulin-resistant are likely to have higher blood sugar levels, as well as higher insulin levels.
To measure insulin resistance, the researchers measured blood sugar levels in the women using the HOMA index, a math formula to assess insulin sensitivity. A normal range is around 2. People with a HOMA score of 2.5 or higher are likely to have insulin resistance.
Overall, 46.95% of the women in the study were classified as insulin-resistant.
The researchers used statistical formulas to account for other factors that might affect progression-free and overall survival, such as age and body mass index (BMI).
The results showed that women who were not insulin-resistant had better progression-free survival:
- progression-free survival was 11.5 months in women with a HOMA score of less than 2.5
- progression-free survival was 8.5 months in women with a HOMA score of 2.5 and higher
This means that women who were insulin-resistant were more likely to have the cancer grow than women who were not insulin-resistant. This difference was statistically significant, which means it was likely due to the difference in insulin levels and not just because of chance.
In the presentation, the researchers didn’t talk about overall survival statistics.
One characteristic of cancer cells is their ability to grow much faster and more uncontrollably than normal.
“We know that growth factors are critical to cancer development and progression,” said Nicoletta Provinciali, M.D., of the Galliera Hospital in Genoa, Italy and presenter of the study. “We know that insulin is an important growth factor for all body tissues, even if we do not know exactly how it affects the development of cancer cells.
“We would now like to see a trial evaluating the effect of physical activity and diet on individual patient metabolism,” she continued. “And we believe that all patients with advanced breast cancer should be counselled on the potential effect of these kind of lifestyle changes."
While genetics play a role in your insulin levels, many people have higher insulin levels because of an unhealthy diet and lifestyle: too much sugar and too many simple carbohydrates combined with not enough exercise. One of the best ways to keep your insulin at healthy levels is to have a healthy diet and lifestyle:
- eat a diet low in added sugar, processed foods, and trans fats
- exercise every day
- maintain a healthy weight
- don’t smoke
- limit or avoid alcohol
If you’ve been diagnosed with metastatic breast cancer, you may want to talk to your doctor about this study. Depending on your unique situation, it may be a good idea to have your blood sugar/insulin levels measured. If your levels are high, you can make the lifestyle changes mentioned above to lower them. There are also medicines you can take.
Stay tuned to Breastcancer.org Research News for the latest information on the relationship between blood sugar levels, insulin levels, and breast cancer prognosis.