What is breast cancer?
Before understanding breast cancer, it is important to become familiar with the structure of the breast. The normal breast consists of breast glands that are connected to the skin surface at the nipple by narrow breast ducts. The glands and ducts are supported by connective tissue composed of fat and fibrous tissue. Blood vessels, nerves and lymphatic vessels leading to lymph nodes make up most of the remaining breast tissue. The breast structures lie beneath the skin and above the pectoral muscles.
As with all other cancers, the abnormal tissues that make up breast cancer are the patient’s own tissues, and the growth of these tissues is not controlled. These cells may also move into other parts of the body where they are not often found. In this case, the cancer is metastatic.
Breast cancer appears in the breast tissue, mainly in the ducts (ductal carcinoma) or glands (lobular carcinoma). Even if the tumor cells are not detected until after they have entered other parts of the body, they are still considered breast cancer and treated as such. These cancers are called metastatic or advanced breast cancers.
Breast cancer often starts as a small, well-defined lump, or as microcalcifications, and then spreads through channels in the breast to the lymph nodes or through the bloodstream to other organs. The tumor may grow and invade the tissues surrounding the breast, such as the skin or chest wall. Different types of breast cancers grow and spread at different rates, with some taking years to spread outside the breast and others growing and spreading rapidly.
Some lumps are benign (non-cancerous), and others may be precancerous. The only safe way to tell a benign lump from a cancer is to have it examined by your doctor through a tissue biopsy.
Men can also develop breast cancer, but male breast cancer accounts for only 1% of all breast cancers. In women, breast cancer is the most common cancer. If eight women live to be at least 85 years old, one of them is expected to develop breast cancer at some point in her life. Two-thirds of women with breast cancer are older than 50 years old, and most of the remaining one-third are between the ages of 39 and 49.
Fortunately, if caught early, breast cancer has a very high cure rate. Localized tumors can usually be successfully treated before the cancer spreads; 9/10 patients survive for at least another 5 years. However, late recurrence of breast cancer is also common.
After the cancer begins to spread, treatment becomes difficult, although treatment can often control the disease for years. Improving screening and treatment options mean that about 8 out of 10 women with breast cancer will survive at least 10 years after their initial diagnosis.
What are the causes of breast cancer?
While the exact cause of breast cancer is not known, its major risk factors are known. However, most women at high risk for breast cancer do not develop breast cancer. On the other hand, 75% of breast cancer patients do not have known risk factors. The most significant risk factors are increasing age and family history. Women with certain benign breast lumps have a slightly increased risk of developing cancer, and women with prior breast or endometrial, ovarian, or colon cancer have a significantly increased risk of developing cancer.
If a woman has a mother, sister, or daughter who has had breast cancer, especially if there is a first-degree relative with the disease, the woman has a 2- to 3-fold risk of developing the disease. The woman’s risk was even higher if the relative had cancer before menopause or had cancer in both breasts. Researchers have identified some of the two genes that cause familial breast cancer – BRCA1 and BRCA2 – and about 1 in 200 women carry one of these genes. Having the BRCA1 or BRCA2 gene makes a woman more likely to develop breast cancer, and although there is no certainty that she will develop breast cancer, her lifetime risk of developing breast cancer is 45% to 80%. These genes also make women more likely to develop ovarian cancer and have been associated with pancreatic cancer, melanoma, and male breast cancer (BRCA2).
Because of these risks, prevention and screening strategies for women with BRCA genes are more aggressive. There are other genes that are thought to contribute to increased breast cancer risk, including the PTEN gene, the ATM gene, the TP53 gene, and the CHEK2 gene. However, these genes have a lower impact on breast cancer risk than the BRCA genes.
In general, women over 50 are more likely to develop breast cancer than younger women.
The link between breast cancer and hormones is clear. Researchers believe that the more estrogen a woman produces, the more likely that woman is to develop breast cancer. Estrogen directs cell division; the more cells that divide, the more likely they are to have some degree of abnormality and therefore may become cancerous.
The levels of estrogen and progesterone produced by women rise and fall over the course of their lives. This is influenced by the age at which a woman starts menstruation (menarche) and stops menstruation (menopause), the average length of her menstrual cycle, and her age at first birth. Breast cancer risk increases if a woman starts menstruating before age 12 (less than a 2-fold increase in risk), has her first child after age 30, stops menstruating after age 55, or is not breastfeeding. The current relationship between birth control pills and breast cancer risk is not clear. Some studies have found that the hormones in birth control pills may not increase breast cancer risk or prevent breast cancer. However, other studies have shown that women who have recently taken the pill have an increased risk of breast cancer, specifically independent of the length of time they have been taking the pill.
Some studies have shown that hormone replacement therapy using a combination of estrogen and progestin leads to an increased risk of breast cancer. In addition, after 7 years of follow-up, it was found that while estrogen use may increase the risk of clotting, estrogen use alone does not increase or decrease the risk of breast cancer formation.
High radiation doses (such as nuclear radiation) or radiation therapy (such as for Hodgkin’s lymphoma treatment) are high risk factors for breast cancer formation 15 to 20 years later. Mammograms do not increase the risk of breast cancer.
There has been a lot of discussion about the relationship between diet and breast cancer. Obesity is a risk factor that requires special attention, especially in postmenopausal women, because obesity alters a woman’s estrogen metabolism. Regular alcohol consumption, especially more than 1 drink a day, also increases the risk of breast cancer. Many studies have shown that women with high dietary fat content, whether red meat or high-fat dairy products, are more likely to develop breast cancer. Researchers speculate that if women reduce their daily caloric intake from fat to less than 20 to 30%, they may reduce their risk of breast cancer.