What are the risks and benefits of annual versus biannual (every 2 years) mammography screenings?

From the Guidelines

Annual screening mammography is recommended for women at intermediate risk, starting no later than 40 years of age, as it provides a greater reduction in mortality compared to biennial screening. The decision between yearly and biannual mammograms involves weighing several important factors, including the benefits of earlier cancer detection and the risks of false positives, overdiagnosis, and radiation exposure. For average-risk women aged 50-74, biannual (every two years) mammograms are generally recommended as they provide a reasonable balance of benefits and risks. However, for women aged 40-49 or those with higher risk factors, such as a family history of breast cancer or genetic mutations like BRCA1/2, yearly mammograms may be more appropriate 1.

The primary benefit of more frequent screening is earlier cancer detection, potentially at more treatable stages. According to the American College of Radiology, annual screening mammography results in a greater reduction in mortality compared to biennial screening, with a 40% reduction in mortality for women 40 to 84 years of age, compared to a 32% reduction for biennial screening 1. However, yearly mammograms come with increased risks, including false positives (leading to unnecessary biopsies and anxiety), overdiagnosis of cancers that might never become life-threatening, and slightly higher radiation exposure over time.

Biannual screening reduces these risks while still providing significant mortality benefit for most women. Personal risk factors should guide this decision, and women with a family history of breast cancer, genetic mutations like BRCA1/2, or previous radiation therapy may benefit more from annual screening 1. The best approach is to discuss your specific risk profile with your healthcare provider to determine the screening frequency that offers the optimal balance of benefits and risks for your situation.

Some key points to consider include:

• The American Cancer Society recommends that women with an average risk of breast cancer should undergo regular screening mammography starting at age 45 years, with annual screening for women 45 to 54 years old, and biennial screening or the option to continue annual screening for women 55 years and older 1.
• The American College of Physicians recommends biennial screening mammography, particularly after age 55 years, as a reasonable option to reduce the frequency of harms, as long as patient counseling includes a discussion that with decreased screening comes some reduction in benefits 1.
• 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 1.

Ultimately, the decision between yearly and biannual mammograms should be based on individual risk factors and a discussion with a healthcare provider to determine the best approach for each woman.

From the Research

Yearly vs Biannual Mammograms: Risks vs Benefits

• The American College of Radiology (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 2.
• For women at higher-than-average risk, the supplemental screening method of choice is breast MRI, and annual mammography is recommended with a variable starting age between 25 and 40, depending on the type of risk 2.
• A study comparing the diagnostic performance of Magnetic Resonance Imaging (MRI), ultrasound, and mammography for detection of breast cancer found that MRI provided an overall sensitivity and specificity of 94.6% and 74.2%, respectively, while mammography showed an overall sensitivity of 54.5% and specificity of 85.5% 3.
• Another study found that mammography alone, and also mammography combined with breast ultrasound, seems insufficient for early diagnosis of breast cancer in women who are at increased familial risk with or without documented BRCA mutation, and that MRI offered a significantly higher sensitivity (91%) 4.
• In terms of cost-effectiveness, screening mammography performed annually on all women beginning at age 40 years has reduced breast cancer deaths by 30% to 50%, and the cost per year of life saved is well within the range for other commonly accepted medical interventions 5.
• MRI screening is also cost-effective for very high-risk women, such as BRCA carriers, and others at 20% or greater lifetime risk, but further studies are needed to determine whether MRI is cost-effective for those at moderately high (15%-20%) lifetime risk 5.

Risks and Benefits of Biannual Mammograms

• There is no direct evidence comparing the risks and benefits of yearly vs biannual mammograms in the provided studies.
• However, the studies suggest that annual mammography is recommended for women at average risk, and more intensive screening is recommended for women at higher-than-average risk 2, 6.
• The benefits of annual mammography include early detection and reduced mortality from breast cancer, but the risks include false positives, overdiagnosis, and radiation exposure 6, 5.

Comparison of Imaging Modalities

• A comparison of the diagnostic performance of MRI, ultrasound, and mammography found that MRI had the highest sensitivity (94.6%) and specificity (74.2%), followed by ultrasound (67.2% sensitivity and 76.8% specificity) and mammography (54.5% sensitivity and 85.5% specificity) 3.
• The study also found that combining the results of all three techniques resulted in a sensitivity of 97.7% and a specificity of 63.3% 3.
• Another study found that MRI had a significantly higher sensitivity (91%) than mammography (33%) and ultrasound (40%) for detecting breast cancer in women at increased familial risk 4.