Risk factors
Simply being female is the most important risk factor for breast cancer.
Although men can and do develop breast cancer, the disease is 100 times more likely to occur in a woman than in a man.
Women are at higher risk of breast cancer because they have much more breast tissue than men do. In addition, the female hormone estrogen promotes the development of breast cancer.
The risk of breast cancer is higher in middle-aged and elderly women than in young women. In the United States, more than three fourths of all breast cancers occur in women aged 50 or older. (Meister., 2000)
Increasing age is one of the strongest risk factors for breast cancer.
Although breast cancer can occur early in life, in general it is a disease of ageing.
For a woman in her 30s the risk is approximately 1 in 250, whereas for a woman in her 70s, it is approximately 1 in 30.
Most breast cancers are diagnosed after the menopause; about 75% of breast cancer cases occur after 50 years of age.
Age is considered to be a likely surrogate for DNA damage accumulated during life. (Neilson., 2009)
Breast cancer is common, affecting about 1 in 8 women at some point during their life, more commonly after the menopause.
There are two genes that BRCA1 (Breast Cancer 1) and BRCA2 (Breast Cancer 2) genes, if mutated, greatly increase an individual’s chance of developing breast and ovarian cancer.
These two genes account for approximately a fifth (20%) of familial breast cancers. It is the most common cause of hereditary breast and ovarian cancer (HBOC).
Women who carry a disease-causing mutation in one of these genes have a significantly higher risk of developing breast and/or ovarian cancer.
There are also other types of cancer associated with a BRCA1 or BRCA2 mutation, including fallopian tube, primary peritoneal, and endometrial (serous) cancer in women, breast and prostate cancer in men as well as pancreatic cancer in both men and women.
Mutations in BRCA1 and 2 are thought to account for approximately 15% of male breast cancers. (Liede et al., 2004)
Obesity and Physical Inactivity
Obesity is an important and potentially modifiable risk factor for breast cancer because of increasing levels of circulating endogenous estrogen from adipose tissue.
In a study among women, postmenopausal women were significantly overweight (p<0.05) with mean BMI 26.4 +/- 2.5 Kg/m2. Body size has opposite influences as a risk factor on breast cancer in premenopausal and postmenopausal women.
Higher body weight is associated with lower risk in premenopausal women whereas risk increases with BMI in postmenopausal women. This suggests the importance of maintenance of weight by modifying lifestyle through healthy dietary habits and increasing physical activities. (Chopra., 2001)
In contrast to leptin, adiponectin, a hormone produced by adipocytes (fat cells) is involved in metabolism and inflammation (Ntuzzi.,2005, Kumada.,2004, Wolf.,2004).
Adiponectin has a strong inverse correlation with fat mass under conditions of obesity, adiponectin concentrations are reduced. For this reason, adiponectin is gaining recognition as an interesting and strongly predictive indicator of abdominal fat and its consequences, such as metabolic syndrome, outcomes which may also be influenced by physical activity.
Among postmenopausal women, an inverse relationship between circulating adiponectin levels and breast cancer risk has been observed. (Miyoshi., 2004)
Exposure to High Doses of Radiation
Women who were exposed to high doses of radiation, especially during adolescence, have an increased risk of breast cancer.
This association has been observed both among atomic bomb survivors and among women who received high-dose radiation for medical purposes.
The low radiation exposures involved in modern x-rays (including chest x-rays and mammograms) have not been associated with any measurable increase in breast cancer risk. ( Lajous., 2009)
Woman’s age at the time of her first full term pregnancy is an established risk factor for breast cancer. Whether the number of pregnancies she experiences in her lifetime is also related to breast cancer risk is less clear.
There is consistent evidence that first pregnancy completed before age 30-35 lowers risk of breast cancer, and that first full-term pregnancy after age 30-35 raises risk.
More limited evidence suggests that women who have many pregnancies may be less likely to develop breast cancer than those who have only one pregnancy. (Yeole., 2003)
Diets high in saturated fats have been associated with increased risk for cancer.
Fat intake, especially saturated fat, is increasing in the middle class in India, although some rural residents traditionally have had a high intake of ghee (clarified butter, high content of saturated fat), as well.
Studies have given equivocal results regarding the link between fat intake and the risk of cancer. (Bosetti., 2001)
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