Breast cancer (Figure 17.32) is the commonest cancer in women in both the UK and the USA, and the second leading cause of cancer deaths in women. The incidence of new cases in the UK is about 41 000 per year and in the USA it is just over 210 000, while the annual incidence worldwide is approximately 1.2 million. It is estimated that about one in nine women will develop breast cancer during their lifetime. Breast cancer also occurs in men, though with a much lower incidence. In the UK, around 250 men are diagnosed with the disease each year and approximately 70 die annually of the disease.
Risk factors for the development of breast cancer include increased age, childlessness, early menarche or late menopause, hormone replacement therapy, being overweight or obese, use of the contraceptive pill and regular consumption of alcohol over a long period of time. Breastfeeding reduces the risk of contracting the disease. Familial breast cancer accounts for 5% of all breast cancers and is related to the inheritance of mutated forms of genes such as the BRCA1 and BRCA2 genes as described.
Breast cancer develops either in the milk-producing glands or in the ducts that deliver milk to the nipple. Symptoms of breast cancer include a new painless lump occurring in a breast, changes in the size or shape of the breast or in the position of the nipple, a discharge from the nipple, an eczematous rash around the nipple or a thickening behind the nipple, puckering or dimpling of the skin of the breast or a swelling or lump in the armpit.
Mammography uses X-rays to locate the position of the potential tumor. Mammography is also used to screen for cancer and, in the UK, this is offered every three years to all women over the age of 50 years. The lump may also be examined by ultrasound or by Color Doppler ultrasound, which gives a picture of the blood supply to the lump. Microscopic examination of cells from a fine needle aspirate of the lump may also be helpful. Alternatively, the lump may be excised under a general anesthetic for pathological examination.
The staging system for breast cancer describes two stages of noninvasive and four stages of invasive breast cancer. Noninvasive stages include ductal carcinoma in situ(DCIS) in which cancer cells are contained within the ducts. If diagnosed at this stage, the disease is almost completely curable. Lobular carcinoma in situ occurs when cancer cells are restricted to the lining of the breast lobules. Stage 1 invasive cancer describes a tumor measuring less than 2 cm diameter, with no spread to the lymph nodes. In Stage 2 invasive cancer the tumor measures between 2 and 5 cm and/or there are affected lymph nodes. In Stage 3 invasive cancer the tumor is larger than 5 cm diameter and may be attached to muscle or skin. The lymph nodes at this stage are usually affected. Stage 4 invasive cancer describes a tumor of any size, the lymph nodes are usually affected and the cancer has metastasized.
A microscopic examination of cancer cells allows their appearance to be graded. Low grade or Grade 1 cancer cells have the appearance of differentiated normal cells, whereas high grade (Grade 3) tumor cells have an abnormal appearance and are characteristic of fast growing and aggressive cancers. The tumor cells may also be examined immunohistochemically or by FISH to detect expression of estrogen receptors or HER2 proteins on their surface. Knowledge of the presence of either of these molecules allows the treatment regimen to be determined more appropriately. Cells with estrogen receptors may be stimulated to divide by naturally occurring estrogen, and hormone therapy is indicated. The HER2 protein is a receptor for the human epidermal growth factor (hEGF). Breast cancers that are positive for HER2 proteins are stimulated to divide by naturally occurring hEGF and some treatments prevent this stimulation and reduce the growth of the cells. In the UK all women with early stage breast cancer are tested for HER2 status of the tumor.
The first line of treatment for breast cancer is to remove the tumor. This may involve excision of the lump and some of the surrounding tissue or it may mean mastectomy. Chemotherapy or hormonal therapy may be given to reduce the size of the tumor prior to excision. During surgery, lymph nodes are also removed from the armpit and used for accurate staging of the tumor. Two to four weeks after excision or mastectomy, radiation therapy is used to destroy any remaining cancer cells. Chemotherapy, using a combination of drugs, may be used before and after surgery. If the tumor cells express estrogen receptors hormone therapy, using drugs such as tamoxifen, is given to block the estrogen receptors or to lower the amount of estrogen in the blood. Tumors that are HER2 positive may be treated with trastuzumab otherwise known as Herceptin which was described.