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2 Cancer Risk Factors and Prevention

      2.1 Introduction

Nearly one‐third of all cancer deaths are related to: (i) individuals having a high body mass index (BMI), which is a measure of body fat based on height and weight of males and females; (ii) eating a diet low in fruits and vegetables; (iii) use of tobacco and alcohol; and (iv) lack of physical activity.

      Cancer prevention therefore includes adopting behaviors and habits that reduce the risk of developing cancer, such as maintaining a healthy lifestyle, avoiding exposure to known cancer‐causing substances, getting recommended cancer screenings, and taking medicines or vaccines that can prevent many types of cancer from developing [1–136].

2.2 Hormones

      Estrogens are a group of hormones that function in human sexual and reproductive development, mostly in women. Although these hormones have essential physiological roles in both sexes, they have also been linked with an increased risk of many cancers. For example, undertaking combined menopausal hormone therapy, consisting of estrogen plus progestin (a synthetic version of the female hormone progesterone), can increase the risk of breast cancer in women. Menopausal hormone therapy using estrogen alone may increase the risk of endometrial cancer, and it is used only in women who have had a hysterectomy. Women considering menopausal hormone therapy should discuss possible risks and benefits with a medical specialist.

      Researchers have discovered that a woman's risk of breast cancer is related to the estrogen and progesterone produced by her ovaries, which are known as endogenous estrogen and progesterone [1–12]. Exposure to a high level of these hormones, or over a lengthy period of time, has been associated with an increased risk of developing breast cancer. High levels of exposure can be caused by starting menstruation early, going through menopause late, having a first pregnancy late in life, or never giving birth. Conversely, however, giving birth is also a protective factor with regard to developing breast cancer.

Regarding cervical cancer, it has been demonstrated that using birth control pills may increase a woman's risk of developing this type of cancer. However, there is also evidence linking birth control pills with lower frequency of other types of cancer, such as endometrial (uterus), colorectal, and ovarian.

2.3 Immunosuppression and Infectious Agents

Infection by certain environmental pathogens can significantly weaken the body's immune system, rendering it less able to detect and destroy cancer cells or to fight off infections that are linked to cancer. Human immunodeficiency virus (HIV) is one such pathogen, and people with this condition are at risk of developing several cancers. Those with HIV/AIDS have an increased risk of cancers that are caused by infectious agents, including Epstein–Barr virus (EBV), hepatitis B (HBV) and hepatitis C (HCV) viruses, infections that can cause liver cancer, human herpesvirus 8 (also known as Kaposi sarcoma‐associated virus), and human papillomavirus (HPV) (Figure 2.1), which has been associated with cervical, anal, oropharyngeal, and other cancers [14–16].

Most of the viruses associated with the possible start of cancer can be spread from one person to another through blood and/or other body fluids. By avoiding “risky behaviors,” people can lower their chance of infection. One important preventative measure is getting immunized. The HBV vaccine is recommended for certain high‐risk adults, including adults who are sexually active but not in a mutually monogamous relationship, people with sexually transmitted infections, intravenous drug users, men who have sex with other males, and health care or public safety workers who might be exposed to infected blood or body fluids. There is also an HPV vaccine, which is recommended for all girls and boys aged 11 and 12, and available to anyone aged 26 or younger who did not avail themselves of the vaccine as adolescents.

Figure 2.1 HPV infection causes several types of cancers.

      Other practical ways to reduce exposure to pathogens linked to cancer development are having safe