What is the difference between breast ultrasound and mammography for breast cancer screening?

Breast Ultrasound vs Mammography for Breast Cancer Screening

Mammography is the gold standard primary screening modality for breast cancer in average-risk women, while ultrasound serves only as a supplemental tool in specific high-risk populations or for diagnostic evaluation—ultrasound should never replace mammography as a primary screening method. 1

Primary Screening: Mammography is Standard of Care

Mammography (including digital breast tomosynthesis) is recommended as the sole primary screening modality for average-risk women, with the strongest evidence supporting biennial or annual screening for women aged 50-69 years 1. The sensitivity of mammography ranges from 77-95% with specificity of 94-97%, and it has demonstrated a 20% relative breast cancer mortality reduction in randomized controlled trials for women aged 50-70 years 1.

• For women aged 50-59 years, mammography screening reduces breast cancer mortality with a relative risk of 0.86 (95% CI, 0.75-0.99), preventing 8 deaths per 10,000 women over 10 years 2
• For women aged 60-69 years, the benefit is even greater with a relative risk of 0.67 (95% CI, 0.54-0.83), preventing 21 deaths per 10,000 women over 10,years 2
• Mammography is the only screening modality with proven mortality reduction in randomized controlled trials 1

Ultrasound: Limited Role as Supplemental Screening Only

There is no consensus supporting ultrasound as a primary or routine supplemental screening method for breast cancer. 1 The European Society for Medical Oncology explicitly states there is no consensus for the use of ultrasound in screening, even for high-risk women with familial breast cancer 1.

When Ultrasound May Be Considered:

• As supplemental screening in high-risk women who cannot undergo MRI (the preferred supplemental modality), according to the American College of Radiology 1, 3
• For diagnostic evaluation of palpable masses, particularly in women under 30 years where it is the preferred initial imaging modality 1
• As an adjunct to mammography in women with dense breasts who desire supplemental screening but cannot access MRI 1, 3
• For characterizing findings detected on mammography or clinical examination 1

Critical Limitations of Ultrasound:

• Ultrasound does not detect most microcalcifications, which are often the only sign of ductal carcinoma in situ 1
• Sensitivity for breast self-examination (which ultrasound parallels in detection capability) ranges only 12-41%, far lower than mammography 1
• No evidence demonstrates mortality reduction with ultrasound screening 1

High-Risk Women: MRI is the Supplemental Modality of Choice

For women at high risk (lifetime risk ≥20%, BRCA mutations, chest radiation before age 30), annual breast MRI combined with annual mammography is recommended, not ultrasound 1, 3. MRI demonstrates:

• Sensitivity of 91-98% when combined with mammography in high-risk women 1
• Incremental cancer detection rate of 8-29 per 1,000 women in elevated-risk populations 1
• 70% lower risk of being diagnosed with stage II or higher breast cancer compared to mammography alone 1

Ultrasound should only be considered for high-risk women who qualify for but cannot undergo MRI due to contraindications, claustrophobia, or lack of access 1, 3.

Diagnostic vs Screening Context

The role of ultrasound differs fundamentally between screening and diagnostic settings:

• Screening context: Mammography alone for average-risk women; mammography plus MRI (not ultrasound) for high-risk women 1, 3
• Diagnostic context: Ultrasound is complementary to mammography for evaluating palpable masses, nipple discharge, or abnormal mammographic findings 1
• Women under 30 with palpable mass: Ultrasound is the preferred initial diagnostic imaging, with mammography reserved for highly suspicious findings 1

Common Pitfalls to Avoid

• Never use ultrasound as a replacement for mammography in any screening scenario—it lacks mortality reduction evidence and misses microcalcifications 1
• Do not offer ultrasound as routine supplemental screening to average-risk women, even those with dense breasts, without first considering whether they truly meet high-risk criteria for enhanced screening 1
• Avoid false reassurance from negative ultrasound in the presence of suspicious clinical or mammographic findings—proceed to biopsy based on the highest suspicion finding 1
• Do not skip mammography in high-risk women receiving MRI—approximately one-third of breast cancers in BRCA2 carriers under 40 may only be detected on mammography 1

Practical Algorithm for Modality Selection

For average-risk women aged 40-74 years:

• Annual or biennial mammography alone 1, 4
• No routine ultrasound 1

For high-risk women (lifetime risk ≥20%, BRCA mutations, chest radiation <30 years):

• Annual mammography starting at age 30-40 (depending on risk factor) 1, 3
• Annual breast MRI starting at age 25-30 1, 3
• Ultrasound only if MRI contraindicated or unavailable 1, 3

For diagnostic evaluation of palpable abnormality:

• Women <30 years: Ultrasound first, mammography if suspicious 1
• Women ≥30 years: Diagnostic mammography first, ultrasound as adjunct 1