Men possess a small amount of nonfunctioning breast tissue (breast tissue that cannot produce milk) that is concentrated in the area directly behind the nipple on the chest wall. Like breast cancer in women, cancer of the male breast is the uncontrolled growth of the cells of this breast tissue.
Breast tissue in both young boys and girls consists of tubular structures known as ducts. At puberty, a girl's ovaries produce female hormones (estrogen) that cause the ducts to grow and milk glands (lobules) to develop at the ends of the ducts. The amount of fat and connective tissue in the breast also increases as girls reach puberty. On the other hand, male hormones (such as testosterone) secreted by the testes suppress the growth of breast tissue and the development of lobules. The male breast, therefore, is made up of predominantly small, undeveloped ducts and a small amount of fat and connective tissue.
How common is male breast cancer?
Male breast cancer is a rare condition, accounting for only about 1% of all breast cancers. The American Cancer Society estimates that in 2008, about 1,990 new cases of breast cancer in men will be diagnosed, and that breast cancer will cause approximately 480 deaths in men (in comparison, over 40,000 women die of breast cancer each year). Breast cancer is 100 times more common in women than in men. Most cases of male breast cancer are detected in men between the ages of 60 and 70, although the condition can develop in men of any age. A man's lifetime risk of developing breast cancer is about one-tenth of 1%, or one in 1,000.
What are causes and risk factors of male breast cancer?
As with cancer of the female breast, the cause of cancer of the male breast has not been fully characterized, but both environmental influences and genetic (inherited) factors likely play a role in its development. The following risk factors for the development of male breast cancer have been identified.
1) Radiation exposure
Exposure to ionizing radiation has been associated with an increased risk of developing male breast cancer. Men who have previously undergone radiation therapy to treat malignancies in the chest area (for example, Hodgkin's lymphoma) have an increased risk for the development of breast cancer.
2) Hyperestrogenism (high levels of estrogen)
Men normally produce small amounts of the female hormone estrogen, but certain conditions result in abnormally high levels of estrogen in men. The term gynecomastia refers to the condition in which the male breasts become abnormally enlarged in response to elevated levels of estrogen. High levels of estrogens also can increase the risk for development of male breast cancer. The majority of breast cancers in men are estrogen receptor-positive (meaning that they grow in response to stimulation with estrogen). Two conditions in which men have abnormally high levels of estrogen that are commonly associated with breast enlargement are Klinefelter's syndrome and cirrhosis of the liver. Obesity is also associated with elevated estrogen levels and breast enlargement in men.
3) Klinefelter's syndrome is an inherited condition affecting about one in 1,000 men. A normal man has two sex chromosomes (X and Y). He inherited the female X chromosome from his mother and the male Y chromosome from his father. Men with Klinefelter's syndrome have inherited an extra female X chromosome, resulting in an abnormal sex chromosome makeup of XXY rather than the normal male XY. Affected Klinefelter's patients produce high levels of estrogen and develop enlarged breasts, sparse facial and body hair, small testes, and the inability to produce sperm. Some studies have shown an increase in the risk of developing breast cancer in men with this condition. Their risk for development of breast cancer is markedly increased, up to 50 times that of normal men.
4) Cirrhosis (scarring) of the liver can result from chronic alcohol abuse, chronic viral hepatitis, or rare genetic conditions that result in accumulation of toxic substances within the liver. The liver produces important binding proteins that affect the transport and delivery of male and female hormones via the bloodstream. With cirrhosis, liver function is compromised, and the levels of male and female hormones in the bloodstream are altered. Men with cirrhosis of the liver have higher blood levels of estrogen and have an increased risk of developing breast cancer.
Epidemiologic studies have shown that men who have several female relatives with breast cancer also have an increased risk for development of the disease. In particular, men who have inherited mutations in the breast cancer-associated BRCA-2 gene have a dramatically increased (about 80-fold) risk for developing breast cancer, with a lifetime risk of about 5%-10% for development of breast cancer. BRCA-2 is a gene on chromosome 13 that normally functions in suppression of cell growth. Mutations in this gene lead to an increased risk for development of breast, ovarian, and prostate cancers. About 15% of breast cancers in men are thought to be attributable to BRCA-2 mutation. The role of the BRCA-1 gene, which has been associated with inherited breast cancers in women, is not as clearly defined for male breast cancers.
What are the different types of male breast cancer?
The most common type of male breast cancer is infiltrating ductal carcinoma, which is also a common type of breast cancer in women. Ductal carcinoma refers to cancers with origins in the ducts (tubular structures) of the breast, and the term infiltrating means that the cancer cells have spread beyond the ducts into the surrounding tissue. On the other hand, lobular cancers (cancers of the milk glands), common in women, are extremely rare in men since male breast tissue does not normally contain lobules.
Other uncommon types of cancers of the breast that have been reported in men include ductal carcinoma in situ (cancer in the ducts that has not spread beyond the ducts themselves), cystosarcoma phylloides (a type of cancer of the connective tissue surrounding the ducts), and Paget's disease of the breast (a cancer involving the skin of the nipple). Some other types of breast cancer that occur in men are named for their growth patterns and microscopic appearance of the cancer cells, including papillary carcinoma, inflammatory carcinoma, and medullary carcinoma.
About 85% of breast cancers in men have estrogen receptors on their cell membranes. Estrogen receptors on the cell membranes allow estrogen molecules to bind to the cancer cells. Estrogen binding to the cancer cells stimulates cell growth and multiplication.
What are the signs and symptoms of male breast cancer?
The most common symptom of breast cancer in men is finding a firm, non-painful mass located just below the nipple. The average size of breast cancer in men when first discovered is about 2.5 cm in diameter. The cancer may cause skin changes in the area of the nipple. These changes can include ulceration of the skin, puckering or dimpling, redness or scaling of the nipple, or retraction (turning inward) of the nipple. Bloody or opaque discharge from the nipple may also occur.
Breast cancer that has spread (metastasized) to the bones may also produce bone pain at the sites of metastases. Advanced breast cancer can also produce symptoms typical of many cancers, including malaise, weakness, and weight loss.