False-Positive Mammography Findings May Increase Breast Cancer Risk

The study’s findings were published April 10, 2012, in the Journal of the National Cancer Institute. Screening mammography is associated with false-positive test results in disease-free women, and those women are typically referred back for routine screening after the initial diagnostic work-up does not reveal cancer. Suspicious findings on screenings leading to false-positives include asymmetric densities, skin thickening or retraction, tumor-like masses, recently retracted nipples or suspicious axillary lymph nodes. It is unknown if women whose mammographic screenings show these results have a higher long-term risk for breast cancer compared to women who at first test negative.

In order to determine if women who test false-positive after mammography screenings have a higher risk of developing breast cancer than those who test negative, My von Euler-Chelpin, PhD, in the department of public health at the University of Copenhagen (Denmark) and colleagues, gathered data from a long-standing population-based screening mammography program in Copenhagen, Denmark, from 1991-2005. They evaluated the risk of breast cancer and ductal carcinoma in situ in women who had received false-positive test results between the ages of 50-69. The age-adjusted relative risk of breast cancer for women who had tested false positive for breast cancer was compared to women who had tested negative.

The researchers found that women who had tested negative for breast cancer had an absolute cancer rate of 339/100,000 person-years at risk, compared to women who tested false positive, who had an absolute cancer rate of 583/100,000 person-years at risk. The relative risk of breast cancer in women with false-positive tests was statistically significantly higher than women who tested negative even at six or more years after the test. However, the researchers cautioned, “the excess breast cancer risk in women with false-positive tests may be attributable to misclassification of malignancies already present at the baseline assessment,” the authors wrote. Thus, new screening techniques such as high-resolution ultrasound and stereotactic biopsy may result in more effective diagnoses and fewer false positives on first screen.

The authors also cautioned that the experience of a false positive may cause anxiety, which may discourage women from attending regular screenings. However, the long-term excess risk of breast cancer in women who tested false positive underscores the need for women to have regular screenings. “Based on the findings in this study, it may be beneficial to actively encourage women with false-positive tests to continue to attend regular screening.”

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