AsianScientist (Sep. 21, 2017) – Scientists in China have discovered a link between body fat distribution and the risk of developing specific subtypes of breast cancer in women. They published their findings in the journal The Oncologist.
Breast cancer is the most common cancer among women in China and the fifth leading cause of cancer-related deaths. Obesity is a well-known risk factor, which can be partly mitigated by lifestyle changes and the use of drugs like Tamoxifen in high-risk women. However, long-term drug use has side effects, and Tamoxifen only works for women whose breast cancer cells possess receptors for the hormone estrogen on their surface (ER-positive). Breast cancers that lack the estrogen receptor (ER-negative) do not respond to Tamoxifen.
In this study, scientists recruited 1,316 Han Chinese women aged between 25 and 70 from 21 hospitals in Northern and Eastern China who were newly diagnosed with breast cancer. They took body measurements and collected data on their reproductive and medical history, including whether they had been diagnosed with ER-positive or ER-negative breast cancer. The women were compared with a control group of healthy in-patients attending the hospitals for a physical examination.
Yu and his colleagues found that women with a high body-mass index (BMI), providing a measure of subcutaneous fat, were more likely to have ER-positive breast cancers, especially if they were premenopausal. In contrast, women with a high waist-hip ratio (WHR), providing a measure of visceral fat, were more likely to have ER-negative breast cancer, especially if they had passed the menopause. This greater risk of developing ER-negative breast cancer for women with a high WHR held even if they did not have a high BMI.
“A possible reason is that subcutaneous fat is involved in estrogen production, which may promote ER-positive breast cancer,” said Yu. “Visceral fat is more closely related to insulin resistance and may be more likely to promote ER-negative breast cancer.”
Higher BMIs were not found to protect the Chinese women from breast cancer before the onset of menopause, in contrast to findings from studies on black and white women.
“I think there are two reasons for this,” said Yu. “First, compared to western women, premenopausal Asian women, including Chinese women, tend to be slender, and fat mass may have a greater impact. Second, Asian women are more likely to become obese by accumulating visceral fat; this is quite different from western countries, where women are more likely to accumulate subcutaneous fat.”
Based on their findings, Yu and his colleagues advise clinicians to evaluate ER-positive breast cancer risk in obese women before prescribing Tamoxifen.
“Considering that Tamoxifen cannot prevent ER-negative breast cancer, women with high WHRs may not benefit,” Yu explained. “And, more interestingly, it is the different patterns of fat distribution, visceral fat and subcutaneous fat, that may contribute to the distinct effects of obesity type, and this speculation provides a novel perspective for further study as to the interaction between obesity and breast cancer.”
He also recommended more research into the effect of other breast cancer risk factors, such as insulin resistance and inflammation, in obese women. Tools for predicting which high-risk women may develop ER-positive and ER-negative breast cancers must also be developed.
“Breast cancer is today becoming pandemic and, contrary to conventional wisdom, the global obesity epidemic is not restricted to industrialized societies. In developing countries like China, the combination of breast cancer and obesity can provoke severe health and economic consequences,” said Professor Eduardo Cazap, director of the Latin America and Caribbean Society of Medical Oncology in Buenos Aires, Argentina, who is a section editor of The Oncologist and was not involved in the study.
“The findings provided by Yu and his colleagues may contribute to improving breast cancer prevention in many countries,” said Cazap.
The article can be found at: Wang et al. (2017) Distinct Effects of Body Mass Index and Waist/Hip Ratio on Risk of Breast Cancer by Joint Estrogen and Progestogen Receptor Status: Results from a Case‐Control Study in Northern and Eastern China and Implications for Chemoprevention.
Source: Wiley; Photo: Shutterstock.
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