Are false positive biopsies for breast cancer common?

False Positive Breast Biopsies Are Common in Breast Cancer Screening

False positive biopsies following breast cancer screening mammography are indeed common, with the majority of biopsies performed after abnormal mammograms yielding benign results. According to the American Cancer Society guidelines, among women who undergo biopsy following a positive mammogram, only 12-78% of these biopsies will reveal cancer, meaning that 22-88% are false positives 1.

Frequency of False Positive Results

The frequency of false positive results varies based on several factors:

• Biopsy rates: According to the U.S. Preventive Services Task Force, 7.0% of women undergoing annual mammography screening will have a false positive biopsy recommendation over a 10-year period, compared to 4.8% for biennial screening 1.

• Overall false positive rates: The cumulative probability of at least one false-positive mammogram over 10 years of screening is strikingly high:

  • 61.3% with annual screening
  • 41.6% with biennial screening 1

• Screening interval impact: Screening every two years rather than annually reduces the cumulative incidence of false positive recalls by about 32% and false positive biopsies by about 31% 1.

Risk Factors for False Positive Results

Several factors increase the likelihood of false positive results:

• First-time mammogram
• Greater mammographic breast density
• Use of postmenopausal hormone therapy
• Use of digital vs. screen-film mammography
• Longer time intervals between screenings
• Lack of comparison mammography images from previous examinations 1

Clinical Implications of False Positive Biopsies

False positive biopsies have several important implications:

1. Psychological impact: False positive results can cause anxiety and distress, though for most women this is short-lived and doesn't affect future screening behavior 1, 2.

2. Additional procedures: False positives lead to follow-up testing and invasive procedures such as breast biopsy, resulting in inconvenience, discomfort, and additional medical expenses 1.

3. Varying pathological significance: Not all false positive biopsies are equal in terms of risk implications. Some reveal high-risk lesions (atypical proliferative changes) that indicate increased future cancer risk, while others show low-risk nonproliferative changes 3.

4. Future cancer risk: Women who have experienced false-positive mammography are at greater risk of interval cancer (cancer detected between screening rounds) and cancer detected at second screening compared to women with normal mammograms 4.

Mitigating Harms of False Positive Results

To reduce the harms associated with false positive results:

• Establish standard post-biopsy follow-up protocols to promptly recognize discordance between clinical suspicion, radiologic impression, and pathologic findings 5
• Use image-guided biopsies when possible, as they have lower false-negative rates compared to non-image-guided procedures 5
• Consider biennial rather than annual screening for average-risk women to reduce false positive rates 1
• Ensure availability of prior mammograms for comparison 1

Patient Communication

Women should be informed about:

• The likelihood of false positive results with screening
• The potential need for additional imaging or biopsy
• The fact that most biopsies will yield benign results

Research shows that women are generally aware that false positive results occur and accept them as part of screening. Most do not regard false positives as an important harm in the context of early breast cancer detection 1.

Conclusion

While false positive biopsies are a common and important consideration in breast cancer screening, most women find the short-term anxiety acceptable given the potential mortality benefit of early detection. Healthcare providers should be transparent about the likelihood of false positive results while emphasizing the overall benefits of appropriate screening.