A family history of breast cancer means that one or more close blood relatives have or had breast cancer. Some families have more cases of breast cancer than would be expected. Sometimes it is unclear whether the family's cancer pattern is due to chance, shared lifestyle factors, genes passed down from parents to children, or a combination of these factors. A family history of breast cancer means that one or more close blood relatives have or had breast cancer. Some families have more cases of breast cancer than would be expected. Sometimes it is unclear whether the family's cancer pattern is due to chance, shared lifestyle factors, genes passed down from parents to children, or a combination of these factors.
Having one first-degree relative (mother, sister, daughter) with breast cancer approximately doubles a woman's risk. The more first-degree relatives with breast cancer, the higher the risk. The risk from second-degree relatives (grandmothers, aunts, nieces) is not as high as that from first-degree relatives.

Genetic mutations are changes in a gene. Some gene changes can increase the risk of certain types of cancer. Inherited gene mutations are passed down from parents to their children. Only a small percentage of breast cancers (about 5-10%) are caused by an inherited gene mutation.
BRCA1 (breast cancer gene 1) and BRCA2 (breast cancer gene 2) are known as tumor suppressor genes because they play a role in controlling the growth of cancer cells. Mutations in the BRCA1 or BRCA2 genes can affect them, so they no longer control the growth of cancer. These mutations are rare and occur in about 1 in 500 people.
Both men and women can inherit a mutated BRCA gene from their mother or father. People who have a gene mutation can also pass it on to their children. If one parent has a mutation in 1 of the 2 copies of the BRCA gene, the child has a 50% chance of inheriting the gene mutation. This also means that there is a 50% chance that the child will not inherit the gene mutation.
Studies show that women with inherited mutations in the BRCA1 or BRCA2 genes have up to an 85% chance of developing breast cancer in their lifetime. Women with these inherited mutations also have a higher risk of developing breast cancer at a younger age (usually before menopause) than other women. Women with a BRCA gene mutation also have a higher risk of developing cancer in both breasts. If they develop cancer in one breast, they have a higher risk of developing cancer in the other breast. The BRCA gene mutation also increases the risk of ovarian cancer in women at any age.
If several members of your family have had breast cancer, talk to your doctor about hereditary breast cancer and genetic testing.

Breast density is an inherited trait. Women with dense breast tissue have a higher risk of developing breast cancer than women with low or absent breast density. Breast density can only be seen on a mammogram, but "dense breasts" make mammogram readings more difficult. On a mammogram, fatty tissue appears dark, while dense tissue appears white like tumors, so it can hide a tumor.

Estrogen is the primary hormone associated with breast cancer. Estrogen affects the growth of breast cells and is believed to play an important role in the growth of breast cancer cells. The type and duration of exposure of cells to estrogen influence the development of breast cancer.

The beginning of menstruation is called menarche. Early menarche is when menstruation starts at a young age (11 years old or younger). Starting menstruation early means that your cells are exposed to estrogen and other hormones for a longer period of time. This increases the risk of breast cancer.

Menopause occurs when the ovaries stop producing hormones, and the level of hormones (mainly estrogen and progesterone) in the body decreases. This causes periods to stop. If a woman enters menopause at a later age (after 55 years old), it means that her cells are exposed to estrogen and other hormones for a longer period of time. This increases the risk of breast cancer. Similarly, menopause at a younger age reduces the time that breast tissue is under the influence of estrogen and other hormones.

Pregnancy interrupts the influence of breast cells on circulating estrogen, which also reduces the total number of menstrual cycles in a woman's lifetime.
Women who have their first full-term pregnancy after the age of 30 have a slightly higher risk of breast cancer than women who have at least one full-term pregnancy at a younger age. Getting pregnant at a young age (for example, before age 20) reduces the risk of breast cancer.
The more children a woman has, the greater the protection against breast cancer.

Women who received radiation therapy in the chest, neck, and underarm areas have a higher risk of developing breast cancer.
This increased risk is particularly noted in women who received treatment for Hodgkin's lymphoma in these areas. The risk of developing breast cancer is higher if radiation therapy for Hodgkin's lymphoma is given before age 30. The risk increases even more if radiation therapy is given during the period of sexual maturation. The risk of breast cancer is significantly increased if chemotherapy is combined with radiation therapy to treat Hodgkin's lymphoma before the age of 15. However, the benefit of cancer treatment generally outweighs the risk of developing a second cancer from radiation therapy.
In the past, medical radiation therapy was used to treat health problems such as tuberculosis, acne, or enlarged thymus gland. Women who received medical radiation therapy in the chest area for these conditions have a higher risk of developing breast cancer.
Many women fear that regular mammography will increase their risk of breast cancer, but modern mammography equipment uses very low doses of radiation compared to the dose used for cancer treatment. The benefits of mammography outweigh the risks of radiation.

Studies show that long-term use of hormone replacement therapy (HRT) increases the risk of breast cancer, especially for HRT that uses estrogen and progestin. Currently, researchers believe that the risks of long-term use of combined HRT outweigh the benefits.

Combined oral contraceptives that contain both estrogen and progesterone may slightly increase the risk of breast cancer, especially among women who have used them for 10 or more years. The higher risk disappears after a woman stops taking oral contraceptives. However, current and recent users (less than 10 years since last use) have a slightly higher risk compared to women who have never used oral contraceptives.

Atypical hyperplasia is a non-cancerous (benign) condition in which there are more abnormal (atypical) cells in the breast tissue. Atypical hyperplasia increases a woman's risk of developing breast cancer.

Drinking alcohol increases a woman's risk of developing breast cancer. Even low levels of alcohol consumption (slightly more than 1 drink per day) can increase a woman's risk. The risk increases with the amount of alcohol consumed.
One possible reason for the link between alcohol and breast cancer is that alcohol is believed to cause high levels of estrogen. Alcohol can also decrease levels of some important nutrients that protect against cell damage, such as folate (a type of vitamin B), vitamin A, and vitamin C.

Obesity increases the risk of breast cancer in postmenopausal women. Studies have shown that women who have never taken hormone replacement therapy and have a body mass index (BMI) of 31.1 or higher have a 2.5 times greater risk of developing breast cancer than those with a BMI of 22.6 or lower.
Ovarian hormones, particularly estrogens, play an important role in breast cancer. Many breast cancer risk factors are believed to be the result of the cumulative estrogen dose that breast tissue receives over time. While the ovaries produce most of the estrogen in the body, after menopause, fat tissue produces a small amount of estrogen. More fat tissue can increase estrogen levels and, therefore, increase the likelihood of developing breast cancer.

Lack of physical activity increases the risk of breast cancer in both pre- and postmenopausal women. Today, a number of studies are examining the impact of exercise on breast cancer.