New study shows differing effects of obesity and metabolic syndrome on breast cancer

A study conducted by the University of Oklahoma and published in the journal CANCER found that both obesity and metabolic syndrome-a cluster of conditions like high blood pressure and high blood sugar-increase the risk of breast cancer, but in differing ways for different subtypes of the cancer.

Breast cancer is one of the most prevalent cancers globally, significantly affecting women. It is the most common cancer among women, with millions of new cases diagnosed each year. According to the World Health Organization (WHO), breast cancer accounts for approximately 24.5% of all cancer cases in women, making it a leading cause of cancer-related deaths.

In the study, a total of 68,132 postmenopausal women without prior breast cancer and with normal mammograms were enrolled in the Women’s Health Initiative randomized clinical trials. The study population consisted of 63,330 women with an entry metabolic syndrome score. At the start, body mass index (BMI) was determined, and the metabolic syndrome score included the following criteria: (1) high waist circumference (≥88 cm), (2) high blood pressure (systolic ≥130 mm Hg and/or diastolic ≥85 mm Hg, or a history of hypertension), (3) a history of high cholesterol, and (4) a history of diabetes. The study outcomes included breast cancer incidence, breast cancer mortality, deaths following breast cancer, and results categorized by hormone receptor status.

The results showed that:

1. Metabolic syndrome is significantly associated with 53% more deaths after breast cancer and a 44% higher breast cancer mortality (the proportion of a population that dies).

2. Metabolic syndrome is also associated with poor prognosis in two specific types of breast cancer: estrogen receptor (ER)-positive and progesterone receptor (PR)-negative.

ER-positive breast cancer occurs when high levels of estrogen in the breast cancer cells help the cancer grow and spread. PR-negative breast cancer means the cancer has no hormone receptors and therefore does not respond to hormone therapy. It also tends to grow faster than hormone-positive cancers.

3. Obesity status is significantly associated with more total breast cancers and more deaths after breast cancer, with higher mortality only in women with severe obesity.

4. Obesity status is also associated with good prognosis in ER-positive and PR-positive cancers. Both can be treated with hormone therapy and tend to grow more slowly than those that are hormone receptor-negative.

“The study showed that obesity and metabolic syndrome independently affect breast cancer risk, each influencing various subtypes differently and impacting diagnosis and mortality. It emphasized the importance of prevention, highlighting the need to address both metabolic syndrome and weight. Metabolic syndrome, which includes high blood pressure, high blood sugar, excess waist fat, and abnormal cholesterol or triglycerides, also raises the risk for cardiovascular disease and diabetes,” said Robert Wild, co-author of the study.

Reference: Chlebowski RT, Aragaki AK, Pan K, et al. Breast cancer incidence and mortality by metabolic syndrome and obesity: The Women’s Health Initiative. Cancer. 2024; 1-10. doi:10.1002/cncr.35318