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Breast Cancer Risk Factors

Anything that affects a person’s absolute risk of developing a disease is called a risk factor. These factors do not cause the disease but increase the chances of getting a disease. Epidemiological studies have identified many risk factors associated with an increased incidence of breast cancer. Other factors are known to lower this incidence. We still do not know the specific factor or factors that may cause breast cancer to develop in some individuals at a specific time but not in others. We have control over some risk factors such as diet and exercise. Other risk factors are out of our control. These include female gender, aging, and family history. Some risk factors have a commonality of increased exposure to hormones. These include early menarche, late menopause, early pregnancy, nulliparity, obesity, and hormone replacement therapy. We will review some of the risk factors associated with breast cancer.

Even if you do not have risk factors you can still develop breast cancer.
The vast majority of breast cancer patients do not have risk factors.

Gender:
A woman by virtue of being a woman has an increased risk to develop breast cancer as compared to a man. This is the most important risk factor for breast cancer. Breast cancer is much more common in women than in men. For 100 women that get breast cancer one man will be diagnosed with the disease.

Age:
As a woman ages the risk of getting a breast cancer increases. Rates begin to increase after the age of 40.The vast majority of breast cancers are diagnosed in women over the age of 50.

Your chance by your current age is:

  age 20
age 30
age 40
age 50
age 60
age 70
Lifetime
  1 in 1,760
1 in 229
1 in 69
1 in 42
1 in 29
1 in 27
1 in 8


Inherited Genetic Mutations:
Inherited mutations only accounts for approximately 5% to 10% of breast cancers in the general population. BRCA1 and BRCA2 are the most well known genes associated with breast cancer. The lifetime risk of developing breast cancer in the presence of a mutation in these genes is between 30% and 90%. The patients and family members affected with these mutations are offered screening preventative strategies, prophylactic surgeries and/or chemoprevention.




Family History:
A family history of breast cancer in a first degree relative (parent, sibling or child) doubles the risk of breast cancer. The risk is 5 times greater with two or more first-degree relatives. It is important to take note that approximately 75% of women who get breast cancer do not have a family history of breast cancer.

Personal History of Breast or Ovarian Cancer:
A person with a history of breast cancer has a higher risk of developing a new breast cancer compared to person without this history. The risk is approximately .5% to 1% per year, up to approximately 16 years. Other cancers have also been linked to breast cancer, including Hodgkin’ disease and ovarian cancer.

Proliferative Breast Conditions:
Women who have proliferative breast conditions have an increased risk of breast cancer. The term proliferative means cells that are multiplying and dividing at a higher rate than normal. A diagnosis of atypical ductal hyperplasia in which abnormal cells are produced carries a much higher risk of breast cancer as compared to proliferative lesions without atypia.

LCIS (Lobular Carcinoma In Situ):
With this condition abnormal cells grow inside the breast lobules. LCIS is a marker of increased risk to develop breast cancer. A woman with this diagnosis can develop either an invasive lobular cancer or invasive ductal cancer.

Reproductive History:
Women who have had an early menarche (the first menstrual period) before the age of 12 and a late menopause (last menstrual period) after age 55 have a higher incidence of breast cancer. This is most likely related to the amount of estrogen the breast is exposed to over a lifetime.

Childbearing:
Women who are nulliparous (a woman who has never borne a child) have a slight increased risk of breast cancer. The higher the number of full pregnancies the higher the protection against breast cancer. Women who had their children below the age of 30 have a protective effect of pregnancy. The risk of breast cancer increases during the first 10 years after the pregnancy but after that it drops below the risk of a woman that never had children.

Race:
White women have a higher incidence of breast cancer than African American, Asian or Hispanic women. Breast cancer is more aggressive in African American women.

High breast Density:
Dense breast tissue is associated with a higher incidence of breast cancer. Breast density refers to the proportion of breast tissue and fat in the breast. The greater the amount of breast tissue in relation to fat the higher the breast density and vice versa. In several studies, women with the highest levels of breast density were found to have a 4 to 6 fold increased risk of breast cancer.

Bone Density:
High bone mineral density in postmenopausal women has been associated with an increased risk of breast cancer. This is most likely related to hormonal factors.

 

Avoidable Risk Factors

Pregnancy:
First pregnancy at a late age (>30 y/o) or women who never had children are at an increased risk for this disease. The function of the female breast is dependent on the proliferation effects of the ovarian hormones, estrogen and progesterone. Estrogen is primarily responsible for elongation and branching of the breast ducts, whereas progesterone is necessary for lobular development and maturation. The high levels of circulating hormones during pregnancy result in the differentiation of the terminal duct- lobular unit (TDLU), which is the major site of malignant transformation of the breast. This process of differentiation is protective against breast carcinoma and the effect is permanent.

Breast Feeding:
A history of breastfeeding seems to protect against breast cancer especially in premenopausal women. The longer the duration of breastfeeding the more protection against breast cancer.

Body Weight:
Obesity and weight gain leads to a higher risk of breast cancer in postmenopausal women. The fatty tissue has an enzyme (aromatase) capable of producing estrogen. The higher the amount of fat cells the higher the production and exposure to estrogen. This is believed to increase the risk of breast cancer. Obesity before menopause appears to decrease a woman’s risk of developing breast cancer. The risk of breast cancer increases if this weight is carried into the postmenopausal years.

Exercise:
A sedentary lifestyle without exercised has been linked to an increased risk of breast cancer. Exercise lowers body weight, lowers estrogen levels, and boosts the immune system. Women who participate in routine strenuous activity and exercise have some protection against breast cancer compared to women who engage in a sedentary lifestyle.

Alcohol:
Epidemiological studies have shown that moderate drinking increases the risk of breast cancer. The exact mechanism by which alcohol causes breast cancer is not yet known, but it is believed to increase the levels of estrogen. Although moderate drinking has been shown to offer some protection against heart disease women should limit their alcohol consumption. Women who have one or more drink of alcohol a day have an increased of breast cancer.

Hormonal Replacement Therapy:
Hormone replacement therapy with combined estrogen and progesterone increases the risk of getting breast cancer. The risk is associated with an increased length of exposure to hormones. The risk starts to rise within the first five years of use. Hormonal replacement therapy is also associated with a higher risk of ovarian cancer, heart disease, stroke, and pulmonary embolism.

Oral Contraceptives:
Oral contraceptives have a modest and temporary effect on a woman’s risk of breast cancer. Women have a slightly higher risk while they are on the pill, but this subsides after they stop taking it. The risk is higher during premenopausal years.

Exposure of Radiation Therapy:
A history of exposure of a high dose of radiation at a young age has been associated with an increased risk of breast cancer. This includes women who were treated with radiation therapy for Hodgkin’s lymphoma at a young age.