Even though previous research has documented that survivors of breast cancer are at increased risk for developing heart disease, how breast cancer and specific treatments increase risk of cardiometabolic risk factors has been less studied. So, in a new study published online in January in the Journal of Clinical Oncology, researchers set out to collect that data (2022; doi: 10.1200/JCO.21.01738). The research includes thousands of women diagnosed with breast cancer and thousands of women without a history of breast cancer who served as matched controls.
"The findings highlight the importance of oncologists talking to their breast cancer patients about their risk for diabetes and high blood pressure and what they can do to reduce that risk," said the study's lead author, Marilyn Kwan, PhD, Senior Research Scientist in the Division of Research at Kaiser Permanente Northern California. In an interview with Oncology Times, Kwan shared her thoughts about the new research.
1 Why conduct this research now and what does it tell us that previous research hasn't?
"Women with breast cancer, especially early-stage breast cancer, are more likely to die of heart disease. However, large, population-based studies in breast cancer survivors on cardiometabolic health problems, such as hypertension and diabetes, are limited.
"Our study compared risk for hypertension, diabetes, and abnormal cholesterol levels in 14,942 women diagnosed with invasive breast cancer compared with 74,702 women without breast cancer of similar age, race, and ethnicity at Kaiser Permanente Northern California. We showed a cumulative high blood pressure incidence rate of 10.9 percent in the breast cancer survivors and 9.3 percent in the women without breast cancer, a difference which was statistically significant. For diabetes, there was also a statistically significant difference in the cumulative incidence rate of 9.3 percent in the breast cancer survivors compared to 8.8 percent in the women without breast cancer."
2 Were there significant differences in cardiometabolic risk factors for women in the various subgroups you looked at?
"We looked at women diagnosed with all stages of invasive breast cancer and compared them to women without breast cancer of the same age, race, and ethnicity. The subgroups consisted of dividing women with and without breast cancer by receipt of individual adjuvant treatments and combination of treatments. These included chemotherapy, left-sided radiation therapy, and/or endocrine therapy. We also examined BMI subgroups of patients who were normal weight, overweight, and obese at the time of their breast cancer diagnosis or the equivalent time in those without breast cancer.
"The diabetes risk was 1.2-1.3 times higher in women whose breast cancer treatments included chemotherapy, left-sided radiation therapy, or endocrine therapy compared with women without breast cancer. And the risk for high blood pressure was 1.1 times higher in women who had left-sided radiation or endocrine therapy compared with women without breast cancer.
"Women who were normal weight at the time of their diagnosis were at higher risk of developing diabetes and high blood pressure than those who were underweight or who [were overweight or obese]. There was no elevated risk of any of the cardiometabolic risk factors in the overweight or obese breast cancer patients when comparing them to those without breast cancer of the same BMI category.
"The reason why normal weight women would have this higher risk is not clear and requires further study. It could be related to what's known as the 'obesity paradox' in breast cancer, with some studies finding better survival in overweight women compared to normal weight women after a breast cancer diagnosis. Being overweight might provide greater metabolic reserves and a more optimal balance of muscle and fat compared to normal weight, which could provide protection against developing hypertension or diabetes."
3 What's the bottom-line message practicing oncologists and cancer care providers should know about your work?
"It is important for breast cancer survivors to hear from their health care providers that they are at risk for these other health problems, that their risk may be higher either from the treatment or the physical consequences of being diagnosed, and that they should do as much as they can to prevent weight gain, exercise, stay adherent to all of their medications, and follow up with their other health care providers.
"[In future work], we would like to determine the best ways to address and mitigate cardiometabolic risk factors in breast cancer survivors, especially in health systems such as Kaiser Permanente. These may include evaluating the impact of lifestyle and clinical interventions in patients at high risk of developing cardiovascular disease."