Currently, more than 180,000 new cases of breast cancer each year in the United States and 46,000 deaths, and it is estimated that one in eight American women who live to age 95 will develop breast cancer. Until 1983, breast cancer was the leading cause of cancer death among women, despite an increased incidence of breast cancer is now second only to lung cancer due to the increase in the number of women develop lung cancer.
Breast cancer is rare before 25 years and rarely before 30 years, the incidence rises sharply after 40 years with a mean and median age of 60. Statistically, the risk of breast cancer is higher in nulliparous women (nuns have a higher incidence), in women who menstruate early and late menopause, and those who have their first pregnancy after age 30. Breastfeeding seems to be protective for the mother. Evidence linking oral contraceptives with breast cancer are rare, some studies suggest a slightly higher incidence among women using oral contraceptives.
A family history (limited to first degree relatives, mother, sister, daughter) of breast cancer increases the risk fivefold. The first degree relatives of women who developed bilateral breast cancer before menopause have a much greater risk. The increased risks resulting from atypical hyperplasia and family history are additive.
The etiology of breast cancer is unknown but probably multifactorial. Genetic factors are suggested by the strong tendency of the family. No method of transmission, suggested that the familial incidence is due either to the action of multiple genes or environmental factors that act on similar members of a family. The mutation of the BRCA-1 and BRCA-2 is believed to cause breast cancer. Hormones are also seen as a role in the etiology of breast cancer. The hormone estrogen has been the most studied because of the epidemiological evidence that prolonged exposure to estrogen (rules early, late menopause, nulliparity, and late pregnancy) increases the risk of breast cancer. Viruses are also suspected of causing breast cancer (for example, the Bittner milk factor is a virus that causes breast cancer in mice).
Breast cancer in humans is extremely rare. It presents with painless breast mass. Histological features are identical to those of ductal carcinoma in women. Despite the small size of breasts in men, the diagnosis of breast cancer in humans is delayed, and 50% of patients have metastases in the axillary lymph nodes at diagnosis. Consequently, breast cancer in humans has a generally worse prognosis than breast cancer in women.