Breast Cancer

Epidemiology of Cancers: Breast Cancer

Description
Virtually all breast cancers are adenocarcinomas and are either ductal (85%) or lobular (15%) ^1,2.

Symptoms

• Breast lumps.
• Changes in size, shape of breast.
• Dimpling of breast skin.
• Nipple inversion, change in the nipple.
• Swelling or lump in the armpit.

Epidemiology

• Worldwide breast cancer is the most common cancer in women and the most common cause of cancer death in women.
• The WHO estimate that around 1 million new cases of breast cancer occur worldwide each year. In 2000 breast cancer accounted for 22% of all new cancers in women (27% in high income countries).
• Significant variation in breast cancer incidence exists between countries. The highest rates are observed in Europe and North America and the lowest rates in Asia and Africa (figure 1).

Table 1. Age Standardised (world) incidence and mortality rates of  female breast cancer (2002 estimates)

Source: Cancer Research UK.

• Migrant studies, have shown that women who move from low to high risk countries or vice versa assume rates of the host country over time (frequently one or two generations), indicating international differences in breast cancer rates are due in part, to environmental and lifestyle differences¹.
• The incidence of breast cancer has been increasing in developed countries. In the UK the age-standardized incidence of breast cancer increased from 75/100,000 women in 1979 to 116/100,000 women in 2002². Reasons for this increase are unclear but may reflect a number of factors including, changes in reproductive patterns, increasing obesity in post-menopausal women and use of postmenopausal hormones¹.
• Overall, breast cancer incidence increases substantially with age. Over 80% of cases occur in women aged  >50, while the incidence among women < 40 years of age  is relatively uncommon¹. However, breast cancer is the most commonly diagnosed cancer in women <35 years².
• The highest incidence rates and number of new cases are seen among women age 50-64².
• In 2002 there were 42,023 new cases of breast cancer diagnosed in the UK.
• In 2004 there were 12,427 deaths in the UK from breast cancer, accounting for 17% of all female deaths. In women aged 35-54 breast cancer is the most common cause of death.  Breast cancer is the second leading cause of cancer death in women after lung cancer².
• Between 1989 and 2004 age-standardized death rates declined from 42/100,000 to 29/100,000 women. Declines in mortality were observed among all age groups.
• The estimated relative five-year survival rate for women diagnosed in England and Wales in 2001-03 was 80% compared with 52% for women diagnosed in 1971-75. Improvements in five-year survival have been greatest in the 50-69 year age group².
• The estimated relative twenty-year survival rate increased from 44% in the early 1990s to 64% for the most recent period.
• Breast cancer in men is rare (around 1% of cases of breast cancer) with around 350 cases registered each year in the UK. 

Risk Factors

Established risk factors¹.

• Age
• Family history in first degree relative
• Benign breast disease
• Mammographically dense breasts
• Age at first birth >30 years versus < 20 years
• Menarche at <12 years versus >14 years
• Menopause at >54 years versus <45 years
• High endogenous oestrogen levels
• Ionizing radiation exposure
• Height
• High body mass index (postmenopausal)
• Post menopausal hormone use

Screening and Prevention
The NHS Breast Screening Programme was introduced in the UK in 1988. All women registered with a GP aged between 50-70 are invited for screening by mammography ever 3 years. Since 2004 women aged over 70 may request mammography every 3 years, butare currently not routinely invited.

Research suggests that the NHS Breast Screening Programme saves and estimated 1,400 lives every year in England³.

The World Health Organization International Agency for Research on Cancer (IARC) concluded that mammography screening for breast cancer reduces mortality and that there is a 35% reduction in mortality from breast cancer among screened women aged50-69 years³.

References

1. Adami, HO, Hunter D, Trichopoulos D, eds. Textbook of Cancer Epidemiology, Oxford University Press: New York, 2002.
    
2. Cancer Research UK.
    
3. NHS Breast Screening Programme (NHSBSP)

© CM Kirwan 2006