What is the number needed to treat (NNT) for breast cancer screening using mammography and clinical breast exams to prevent one death from breast cancer?

From the Guidelines

The number needed to treat (NNT) for breast cancer screening using mammography to prevent one death from breast cancer is approximately 1,000 women, as clinical breast exams are not recommended for screening due to lack of mortality benefit and potential harms. This means that about 1,000 women need to be screened regularly over a period of about 10 years to prevent one breast cancer death, as suggested by the American College of Physicians guidance statement 1. The NNT varies somewhat based on the age group being screened, with slightly better effectiveness in women aged 50-74 compared to younger women aged 40-49.

According to the most recent and highest quality study, annual screening mammography beginning no later than 40 years of age for women at intermediate risk is recommended to maximize the benefits 1. The study also suggests that women should continue screening mammography as long as they remain in overall good health and are willing to undergo the examination and subsequent testing or biopsy, if an abnormality is identified.

Some key points to consider when interpreting the NNT include:

• The benefits of screening mammography, including reductions in breast cancer mortality and treatment morbidity 1
• The risks of screening mammography, including false-positive recalls and biopsies, overdiagnosis, and patient anxiety 1
• The importance of individualizing screening decisions based on a woman's risk factors, preferences, and values 1
• The lack of evidence supporting the use of clinical breast exams for breast cancer screening in asymptomatic women at average risk 1

Overall, the NNT for breast cancer screening using mammography highlights the importance of weighing the potential benefits and harms of screening and making informed decisions based on individual patient factors and preferences.

From the Research

Breast Cancer Screening and NNT

• The number needed to treat (NNT) for breast cancer screening using mammography and clinical breast exams to prevent one death from breast cancer is not directly stated in the provided studies.
• However, the studies suggest that regular screening can significantly reduce breast cancer mortality, with a mortality reduction of 40% possible with regular screening 2.
• The American College of Radiology (ACR) recommends annual mammography screening starting at age 40 for women of average risk, which provides the greatest mortality reduction, diagnosis at earlier stage, better surgical options, and more effective chemotherapy 2, 3.
• The benefits of screening should be considered along with the possibilities of recall for additional imaging and benign biopsy and the less tangible risks of anxiety and overdiagnosis 2, 4.
• A study on BRCA1 and BRCA2 gene mutation carriers found that alternating digital mammography and magnetic resonance imaging (MRI) starting at age 25 years provided the highest life expectancy, but also produced the highest number of false-positive screens per woman 5.

Screening Recommendations

• The ACR recommends annual screening beginning at age 40 for women of average risk and earlier and/or more intensive screening for women at higher-than-average risk 6.
• Women with genetics-based increased risk, those with a calculated lifetime risk of 20% or more, and those exposed to chest radiation at young ages are recommended to undergo MRI surveillance starting at ages 25 to 30 and annual mammography 6.
• Women diagnosed with breast cancer before age 50 or with personal histories of breast cancer and dense breasts should undergo annual supplemental breast MRI 6.

Mortality Reduction

• A mortality reduction of 40% is possible with regular screening 2.
• The death rate from breast cancer in the US has declined by at least 38% since 1990, with much of this change attributed to early detection with mammography 3.