Male Breast Cancer (cont.)
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.
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.
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.
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.
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.
Familial predisposition
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.
Next: What are the different types of male breast cancer? »
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