Although various radiographic modalities are readily available to identify lesions that are suspicious for breast cancer, mammography remains the mainstay of breast cancer screening. Role of breast sonogram is confined mainly to the diagnostic follow-up of a mammographic abnormality because it may help clarify features of a potential lesion. The role of magnetic resonance imaging (MRI) for breast cancer screening is still evolving; currently MRI screening, in combination with mammography, is reserved to the screening of high-risk patients only. [1, 2, 3, 4, 5]
In 2015, an estimated 231,840 new cases of invasive breast cancer were diagnosed, along with an estimated 60,290 additional cases of in situ breast cancer. Only lung cancer accounts for more cancer deaths among women. 
Overall breast cancer death rates decreased 36% from 1989 to 2012, because of both improvement in treatments and earlier detection. 
The lifetime risk of being diagnosed with breast cancer is 12.3%, or 1 in 8.  Due to the magnitude of the disease, its psychosocial impact, and associated morbidity and mortality, screening for early diagnosis forms a pivotal part of the struggle against this cancer.
According to the National Health Interview Survey, 69% of women 45 years and older have had a mammogram within the past 2 years. Since 1987, the prevalence of women 40 years and older who have had a mammogram has increased from 29% to 70%. 
According to the U.S. Preventive Services Task Force, the number of breast cancer deaths averted by screening and early treatment increases with age: over a 10-year period, screening 10,000 women aged 60-69 years will result in 21 fewer deaths from breast cancer; 8 fewer deaths in 10,000 women 50-59 years; and 3 fewer deaths in 10,000 women 40-49 years. 
In studies, mammography has clearly been shown to increase the detection of breast cancer at an earlier stage.  Based upon consistent data from multiple randomized trials, a strong consensus has been developed in favor of routine screening mammography for all women aged 50-69. Consensus, however, is not as strong in favor of routine screening among women aged 40-49 or women over the age of 70, and in terms of how frequently these patient populations should be screened.
Based upon pooled data form 8 trials, the United States Preventive Services Task Force (USPSTF) has given an estimate that 1904 women aged 39-49 (credible interval, CrI 929 to 6378 women) would need to be screened to prevent one death from breast cancer after at least 11 years of observation, compared to 1339 women in their 50s (CrI 322-7455) and 377 women in their 60s (CrI 230-1050).  Moreover, false-positive readings are more common in younger women, both because the tests are less specific and because breast cancer occurs less commonly in that population. [8, 9]
Women with an average risk of breast cancer should undergo regular screening mammography starting at 45 years of age.
Women 45-54 years of age should be screened annually.
Women ≥55 years should transition to biennial screening or have the opportunity to continue screening annually.
Women should have the opportunity to begin annual screening between the ages of 40 and 44 years.
Women should continue screening mammography as long as their overall health is good and they have a life expectancy ≥10 years.
The ACS does not recommend clinical breast examination for breast cancer screening among average-risk women at any age.
The USPSTF recommends biennial screening mammography for women aged 50-74 years of age
The decision to start screening mammography in women prior to age 50 years should be an individual one.
Women who place a higher value on the potential benefit than the potential harms may choose to begin biennial screening between the ages of 40 and 49 years.