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 eightyfold) 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.
Finasteride use
Finasteride (Propecia, Proscar), a drug that has been used to treat benign prostatic hyperplasia and to prevent prostate cancer, may be associated with an increased risk for male
breast cancer. During clinical trials for the drug, no increased risk was shown. However,
over 50 cases of male breast cancer have been reported worldwide in men taking the
drug. Further studies are needed to clarify whether a causal relationship between the drug
and the disease actually exists.
http://www.medicinenet.com/male_breast_cancer/page2.htm#what_are_causes_and_risk_factors_of_male_breast_cancer