obesity and cancer

 

The ever-growing obesity epidemic in the United States affects an estimated 93.3 million adults and decreases the health and life span of the affected individuals [1]. Obesity is defined as having a BMI (body weight in kg/ height2) of ≥30 kg/ m2 and is associated with a plethora of comorbidities, including breast cancer[2].

In postmenopausal women, those with BMI and weight in the highest quintile showed a 41- 57% higher risk for breast cancer than those in the lowest quintile [3]. In alignment with the aforementioned study, increased body fat was also shown to increase the risk for developing breast cancer [4]. In addition to increased susceptibility for the development of breast cancer, obesity is also associated with poorer prognosis. In comparison to normal weight individuals, obese patients displayed tumors that were more advanced in stage and grade at diagnosis. Obese patients are also at higher risk for breast cancer recurrence and poorer survival than lean individuals [5, 6]. It should be of note that the associations between obesity and breast cancer risk and prognosis are mostly confined to postmenopausal cases.

Although the mechanism by which obesity affects breast cancer remain uncertain, few theories have been postulated. For one, estrogen is the primary female hormone and has been implicated in breast cancer. Previous study has shown individuals with estrogen levels in the highest fourths to have a twofold increase in breast cancer risk in comparison to individuals with estrogen levels in the lowest fourths. Additionally, individuals with breast cancer displayed higher estrogen levels than health individuals [7]. In contrast to premenopausal women who synthesize estrogen in the ovary, postmenopausal synthesize estrogen in fat tissues. Therefore, increased body fat in obese individual contributes to higher estrogen levels, which in turn increase the risk of breast cancer [8]. Another hormone suggested to mediate the link between obesity and breast cancer is leptin. Leptin is predominately produced by fat cells and the amount of leptin found in the body is proportional to fat mass. In addition to its well-known roles in promoting satiety and inhibiting hunger, leptin has also been suggested to play a role in breast cancer. One study showed women with invasive breast cancer to have higher leptin levels than healthy subjects. The same study also showed an association between higher leptin levels and increased risk for developing breast cancer. Cancer can result from increased growth and division of abnormal cells, otherwise known as cell proliferation. Leptin may increase the risk of breast cancer by promoting cell proliferation. Furthermore, leptin has been shown to increase estrogen synthesis by increasing aromatase, one of the key enzymes in estrogen production. In turn, increased levels of estrogen, as previously mentioned, can increase the risk of breast cancer [9].

Given that obesity is associated with increased risk of breast cancer and poorer prognosis, it may be easy to assume that weight loss could prevent the development of breast cancer and improve prognosis. In fact, weight loss has been shown to decreased breast cancer risk in postmenopausal women [10]. Furthermore, a study investigating exercise and cancer risks showed exercise in adulthood to reduced breast cancer risk by 32% and exercise during adolescent to reduce the risk by 16%. Exercise during both adolescence and adulthood could decrease breast cancer risk up to 64% [10]. However, the effects of weight loss on breast cancer prognosis remain unclear. In addition to the protective effects of weight loss on breast cancer risk, weight loss as little as 5% can have other health benefits, such as reducing risks of heart disease and diabetes. Although the benefits of weight loss are many, it is easier said than done. As if weight loss wasn’t already difficult, treatment options such as chemotherapy and corticosteroids can promote weight gain in breast cancer patients, making it even difficult to loss weight. Weight can be managed with a healthy diet and exercise and a weight management plan can be made in consultation with a doctor or dietician.

 

  1. Prevalence of Obesity Among Adults and Youth: United States, 2015–2016, CDC, Editor.
  2. Mitchell, N.S., et al., Obesity: overview of an epidemic. Psychiatr Clin North Am, 2011. 34(4): p. 717-32.
  3. Trentham-Dietz, A., et al., Body Size and Risk of Breast Cancer. American Journal of Epidemiology, 1997. 145(11): p. 1011-1019.
  4. Lahmann, P.H., et al., A prospective study of adiposity and postmenopausal breast cancer risk: the Malmo Diet and Cancer Study. Int J Cancer, 2003. 103(2): p. 246-52.
  5. Protani, M., M. Coory, and J.H. Martin, Effect of obesity on survival of women with breast cancer: systematic review and meta-analysis. Breast Cancer Res Treat, 2010. 123(3): p. 627-35.
  6. Ayoub, N.M., et al., Impact of Obesity on Clinicopathologic Characteristics and Disease Prognosis in Pre- and Postmenopausal Breast Cancer Patients: A Retrospective Institutional Study. J Obes, 2019. 2019: p. 3820759.
  7. Missmer, S.A., et al., Endogenous estrogen, androgen, and progesterone concentrations and breast cancer risk among postmenopausal women. J Natl Cancer Inst, 2004. 96(24): p. 1856-65.
  8. Cleary, M.P. and M.E. Grossmann, Obesity and Breast Cancer: The Estrogen Connection. Endocrinology, 2009. 150(6): p. 2537-2542.
  9. Wu, M.H., et al., Circulating levels of leptin, adiposity and breast cancer risk. Br J Cancer, 2009. 100(4): p. 578-82.
  10. Chlebowski, R.T., et al., Weight loss and breast cancer incidence in postmenopausal women. Cancer, 2019. 125(2): p. 205-212.