JAMA: History of breast cancer increases risk but weakens mammo detection

Mammogram reveals increased density (arrow) of the right breast.
Image source: Indian J Radiol Imaging 2010 May;20(2):98–104.
Mammography is significantly less sensitive in the detection of breast cancer in women with prior malignancies, leading researchers at once to call for diligent screening in this especially high-risk group and for further investigation into adjunct cancer screening methods, according to a study published Feb. 23 in the Journal of the American Medical Association.

Women with personal history of breast cancer (PHBC) are significantly more likely to experience additional malignancies, and while mammography is generally recommended in this group, little is known about the effectiveness of early screening in PHBC-women.  “Valid estimates of the accuracy of screening mammography are therefore needed to guide clinical practice and policy in this setting and to inform clinicians and PHBC women of expected screening outcomes,” explained Nehmat Houssami, MBBS, PhD, of the screening and test evaluation program at the University of Sydney’s School of Public Health, Sydney Medical School (Australia) and colleagues.

“This study examines the accuracy and outcomes of screening mammography and factors associated with screening outcomes in women with a PHBC,” continued Houssami and colleagues. Using data from the Breast Cancer Surveillance Consortium (BCSC), the researchers examined mammography interpretations and 12-month follow-up for 58,870 mammograms (19,078 women) with PHBC and 58,870 mammograms in 55,315 women without prior histories.

The sample disparity was utilized to enable the researchers to compare mammogram accuracy while controlling for known risk-factors, including age and density. The additional non-PHBC women, therefore, enabled matched comparisons of at least 1,000 mammograms according to these confounding variables. Women with histories of breast cancer presented with 655 second cancers (499 invasive, 156 ductal carcinoma in situ), compared with 342 cancers (285 invasive, 57 ductal carcinoma in situ) within one-year follow-up of mammography. Ductal carcinoma in situ occurred at a 7.1 percent higher rate in PHBC women. Overall cancer rates were 10.5 per 1,000 for women with PHBC and 5.8 per 1,000 in women without personal histories.

The sensitivity of mammography in the PHBC group was 65.4 percent, compared with 76.5 percent in the non-PHBC group, while women with histories had a 2.3 percent chance of abnormal mammogram results, compared with 1.4 percent in women without prior histories. The authors pointed out that this lower sensitivity among the PHBC group was most dramatic and attributable to invasive cancer, at 61.1 percent in PHBC women and 75.7 percent in the matched group.

Specificity between the two groups was nearly equal, although almost twice as many PHBC women required additional mammography views, ultrasound or fine-needle aspiration, biopsy or surgical consultation.

Among PHBC screens, detection was more sensitive for women whose first cancer was ductal carcinoma in situ relative to invasive cancer. This relationship held whether the second cancer was ductal carcinoma in situ or invasive.

In addition, sensitivity was more than 10 percent lower in the detection of second cancer among women whose first cancer occurred within the last five years (60.2 pecent), compared with women whose cancer had presented more than five before the last screening (70.8 percent).

Among PHBC women, the authors observed that specificity was higher and the rate of abnormal interpretation lower in women who had received mastectomies instead of breast-conserving surgery.

Houssami and colleagues also found that women who had undergone chemotherapy were significantly less likely to have their cancer detected by mammography, with an odds ratio of .45, compared with women without histories of systematic therapies. “We were surprised to find higher mammography sensitivity (evident for ipsilateral and contralateral cancer) in women who had not received systemic therapy, for whom underlying cancer rates were also higher compared with those who received chemotherapy or endocrine therapy,” the authors explained. When controlling for all confounding risks, the lower sensitivity held among patients with previous chemotherapy.

Houssami and co-authors offered several explanations for mammography’s reduced sensitivity among PHBC women. “First, PHBC women may have different host factors predisposing them not only to risk of a second breast cancer but also to breast cancers that are less likely to be detected with screening, possibly because of more rapid growth or other tumor biology characteristics. Second, they may partly reflect higher breast awareness by PHBC women, who might seek help promptly for breast symptoms.”

“To our knowledge, we report the first comprehensive study of accuracy measures of mammography screening in PHBC women that includes both ipsilateral and contralateral breast screening outcomes, providing evidence to inform practice and guide recommendations on mammography screening in PHBC women,” the authors continued. “Key findings are that mammography screening in PHBC women detects cancers at an early stage but has lower accuracy than screening in women without PHBC, despite a higher rate of additional evaluation and higher underlying cancer rates in PHBC women.”

The authors said that their findings neither support nor negate a role for adjunct screening in PHBC women, but emphasized that adjunct screening, as well as alternative screening approaches and biomarkers, strongly merit further study.

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