Epidemiology

Oxford American handbook of oncology. Second Edition. Oxford University Press (2015)


Key facts about breast cancer

  • The risk of breast cancer correlates with socioeconomic status.
  • The lifetime risk in the United States for developing invasive breast cancer is approximately one in eight women and is among the highest in the world.
  • Breast cancer is the most common female cancer in the United States, with a projected incidence of 232340 cases in 20,3 representing 29% of all malignancies
  • After decades of steady increases, the incidence of breast cancer stabilized from 2001 to 2003. This stabilization has been attributed to saturation of screening mammography as well as decreased use of hormone replacement therapy (HRT).
  • In the United States, breast cancer is second only to lung cancer as a leading cause of cancer-related deaths among women. There are 39620 deaths projected from breast cancer in 20,3 representing 14% of all cancer-related deaths.
  • Breast cancer is the leading cause of cancer mortality among women aged 20–59 years.
  • Breast cancer mortality rates have declined since 1975 in response to improved screening with earlier diagnosis and improved adjuvant treatment.
  • Male breast cancer is rare, with approximately 2240 new cases and 410 deaths projected in the United States in 20,3.

Etiology

Several risk factors have been identified by epidemiological studies.

Age

  • Breast cancer is very rare before the age of 20 and rare below 30 years.
  • Incidence of breast cancer doubles every 10 years until menopause.
  • After 50 years, the rate of increase slows and in some countries plateaus.

Geography

  • There is a 7-fold variation in incidence between high- and low-risk countries, with the highest rates in Northern America and Western Europe and the lowest rates in Asia and Africa.
  • Migrants from low-incidence countries assume the risk in the host country within two generations.

Age at menarche and menopause

  • Early menarche and late menopause increase the risk.
  • Ovarian ablation before 35 years reduces the risk of breast cancer by 60%.
  • Menopause after the age of 55 years doubles the risk.

Age at first pregnancy

  • Nulliparity and late age at first pregnancy increase the risk.
  • Awoman whose first pregnancy is at age 30 years has double the risk of breast cancer compared with a woman whose first pregnancy is at <20 years.

Family history

Inheritance of genetic mutations, such as BRCA1, BRCA2, p53, ATM, CHEK2, and PTEN, accounts for approximately 5%–10% of breast cancers.

Exogenous estrogens

  • Use of oral contraceptives for >4 years before the first pregnancy increases the risk of premenopausal breast cancer.
  • Combined HRT preparations increase the risk of breast cancer.
  • The use of unopposed estrogens in HRT has a less clear effect.

Diet

Associations have been shown with high dietary fat intake, obesity, and alcohol consumption.

Benign breast disease

Previous breast surgery for severe, atypical epithelial hyperplasia is associated with a 4-fold increase in risk.

Radiation

  • Exposure to ionizing radiation at an early age, e.g., treatment of Hodgkin’s disease.
  • Mammographic screening is associated with a decrease in breast cancer deaths but the effects of screening younger women (<50 years) are uncertain.

Male breast cancer

  • Peak incidence is 10 years later than in women.
  • It may occur in association with Klinefelter’s syndrome.
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