Breast cancer occurs when a cell within a breast undergoes changes that cause it to grow and divide uncontrollably. The tumor that develops from this will destroy tissue around it. Any tissue in the breast can be affected. Usually the cancer arises from tissue that forms milk ducts. Both women and men can develop breast cancer, but it is very rare in men.
What is going on in the body?
A tumor in the breast does not affect the bodily function of the breast. For example, the breast may remain sensually active. It can change with the menstrual cycle or pregnancy and can produce breast milk. A tumor will cause destruction of tissue within the breast. Spread of the tumor to other parts of the body can cause death.
Cancer of the breast can be detected when it grows large enough to either be felt or seen on a mammogram. Sometimes a tumor isn't found for many years. The tumor may distort the shape of the breast or the texture of the skin as it becomes larger. This is because surrounding tissues become fixed to the tumor. The tumor will grow through the breast to the outer skin if left untreated.
Cancer cells can also enter specialized channels in the breast called lymphatics. Cancer cells travel through the lymphatics to the lymph nodes to form tumors. This most commonly occurs in lymph nodes under the armpit or within the chest. This may occur when the tumor has grown large, but it can also happen sooner.
Cancer cells can also spread, or metastasize, to other parts of the body through the bloodstream. This can occur when the tumor is large or small. These cells can travel to other tissues and form new tumors. Breast cancer is most often spread to the bones, lungs, brain, and liver. However, any tissue can be affected.
What are the causes and risks of the disease?
The risk for any woman to develop breast cancer is significant, about 1 in 9 over a lifetime. Breast cancer is also seen in men but is much less common. About 5% to 10% of all breast cancers may be related to genes that are passed through families, called BRCA1 and BRCA2. Research has shown that women are also at greater risk of developing breast cancer if the following conditions apply.
They have a personal history of breast cancer in the other breast.
They have close blood relatives, like a mother or sister, who developed breast cancer before menopause.
They have a history of certain changes in the breast tissue, including a condition known as atypical hyperplasia.
There is evidence that the following conditions also contribute to a higher risk for breast cancer:
beginning menstruation before age 12
experiencing menopause after age 55
having a first child after age 30, or not having children
having denser breasts
receiving radiation therapy to the breast before age 30, especially for Hodgkin's lymphoma
using diethylstilbesterol, or DES, during pregnancy
using estrogen, such as hormone replacement therapy for menopause
using oral contraceptives for birth control, if there is a strong family history of breast cancer
Other risk factors have been tentatively identified, but need more study. They include the following:
eating a diet high in fat
using hormones such as progesterone
working a night shift
Women who smoke are more likely to develop breast cancer that is estrogen-receptor negative. These women don't benefit from antihormone therapy. They generally have a poorer outcome from the cancer.
Women who breastfeed their children may lower their risk for breast cancer. However, a woman may have every risk factor and never develop breast cancer. A woman may have no risk factors and develop breast cancer. At this time it is not possible to predict with absolute accuracy who will and who will not develop breast cancer.