A COMPREHENSIVE REVIEW ON THE METABOLIC INTERPLAY BETWEEN OBESITY AND BREAST CANCER

Abstract

Obesity is defined as abnormal or excess accumulation of fat which poses a significant risk to health. A body mass index (BMI) of >= 30 kg/m^2 is considered obese. Obesity causes various fatal diseases and health conditions which include stroke, hypertension, dyslipidemia and a varying range of malignancies such as breast cancer [1]. Using these criteria, multiple epidemiological studies have found that the global obesity rate has risen dramatically in recent decades [2]. Since 1980, in at least 73 countries, the number of obese people has more than doubled. It has affected 108 million children and 604 million adults in 2015, reflecting a 5% prevalence among children and a 12% prevalence among adults. The growing number of obese people has a direct impact on population health. As per the 2016 data, approximately 1.9 billion adults aged 18 and up were overweight and 650 million of these adults were obese [1]. It was recently estimated that overweight and obesity led to 120 million disability-adjusted life-years (DALY) and 4.0 million deaths, accounting for nearly 7% of all fatalities Worldwide [1]. Many other epidemiologic studies have found that weight gain, as well as the associated metabolic disturbances that characterize obesity, result from a disruption in energy balance, causing tissue stress and dysfunction, which causes a variety of fatal diseases and health conditions such as stroke, hypertension, dyslipidemia, osteoarthritis, and a variety of malignancies such as breast cancer [2,3,4].

Breast cancer is the most prominent diagnosed cancer in women, seen across the globe. The interconnection between obesity and breast cancer is a complicated relationship in both premenopausal and postmenopausal women [2,3]. Breast cancer is predicted to kill approximately 41,760 women and 500 men in 2019. Obesity and breast cancer have a convoluted association in both premenopausal and post- menopausal women [3]. Literature observations indicate that the effect of obesity on breast cancer risk is dependent on the menopausal status, disease subtype, and hormone replacement therapy (HRT) [2,3,4].

In this paper an overview is provided on how obesity affects breast cancer differently in premenopausal women and postmenopausal women. This review focuses on the potential mechanism that explains the interplay between obesity and breast cancer with special focus on the levels of estrogen [5,6], altered signaling pathways of insulin/ IGF1 [7], regulation of inflammatory factors, influence of gut microbiota [8] and the act of adipokines (leptin, adiponectin, serum amyloid A) [9]  as a bridge way between obesity and breast cancer [2,3].

Many epidemiological studies have reported evidences of the direct link between weight gain and  increase of cancer risks [10]. We discuss the importance of total energy intake, dietary composition and physical exercise which need to be maintained to lower the risk of breast cancer. Better understanding of the mechanism linking obesity and breast cancer will lead to the development of biomarkers and improve therapy targeted intervention to undermine cancer risk in the future.

Despite substantial studies on the various aspects of obesity on general health and cancer, in

in particular, major gaps in our understanding of processes and correlations remain. A better

understanding of the mechanisms that link obesity and breast cancer would lead to the

development of more effective targeted therapies, reducing cancer risk in the future [11].