**Chapter 1** Obesity and Breast Cancer

*Abdullah Şişik, Hasan Erdem, Muhammed Said Dalkılıç, Mehmet Gençtürk, Merih Yılmaz and Selim Sözen*

#### **Abstract**

Obesity is associated with a higher risk of chronic diseases. Breast cancer is one of the malignancies, which has been related to obesity. Patients with a BMI more than 35 kg/m2 had an 86% greater risk of having breast cancer than those with a normal BMI. Every 5 kg/m<sup>2</sup> rise in BMI has also been demonstrated to increase the risk of postmenopausal breast cancer. Obese people have poorer outcomes in terms of lymph node positivity, disease-free survival, and overall survival, according to research. Leptin, whose circulating levels rise in proportion to BMI and body fat reserves, is usually regarded as the primary driver of the intricate web that connects obesity and breast cancer. The number of studies examining the association between leptin activity and breast cancer genesis and behavior is growing. The effectiveness of bariatric surgery on lessening the risk of developing breast cancer has been proven.

**Keywords:** breast cancer, leptin, obesity, bariatric surgery

#### **1. Introduction**

Obesity prevalence is rapidly increasing in many developed and developing countries. Obesity is related to an increase in the risk of chronic diseases. Obesity is associated with type 2 diabetes, hypertension, cardiovascular disease, and a variety of cancers. Breast cancer is another malignancy that has been related to obesity [1, 2].

American Institute for Cancer Research (AICR) reported that 13 cancers, including postmenopausal breast cancer, colorectal cancer, endometrial/uterine cancer, esophageal adenocarcinoma, gallbladder cancer, stomach cancer, hepatocellular cancer, meningioma, multiple myeloma, ovarian cancer, pancreatic cancer, kidney cancer, and thyroid cancer, were associated with obesity [3, 4].

Breast cancer is one of the most frequently diagnosed cancers among women worldwide. It is known that breast cancer has a worse prognosis and higher mortality rates in obese women [5, 6]. Hyperinsulinemia, estrogen signaling, inflammation, and adipokine expression hypotheses have been proposed for the mechanism of action of obesity in breast cancer patients [7, 8]. At this point, the concept of adipokines is emerging. Despite being primarily produced by adipocytes, adipokines, which are endocrine, paracrine, and autocrine mechanisms produced in a variety of different cells, influence the development of malignancies in obese people [8]. Leptin, an adipokine, plays an important role in the relationship between obesity and breast cancer [9, 10].

### **2. Breast carcinoma**

Classification of breast carcinoma is based on clinicopathological features and expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Approximately 70% of breast cancers consist of tumors that express hormonal receptors.

Genetic profile, age at menarche and menopause, parity, age of first child, past cancer occurrence, and lifestyle are the most important risk factors for breast cancer. However, BRCA1/2 mutations account for approximately 5–10% of cases [11]. Also, obesity, metabolic syndrome, alcohol, and hypercholesterolemia are the other risk factors for breast cancer [12]. Despite all the advances in medical oncology in people with breast cancer, fatal metastases may occur even years after surgical treatment [13, 14]. Bone, lung, and brain are the primary areas of metastasis. The invasionmetastasis process takes place in successive steps. These steps are defined as local invasion, intravasation, circulation survival, attachment and extravasation in distant organ regions, creation of micrometastases, and metastatic growth [15, 16]. Failure at any step will end the metastasis process.
