Screening Mammograms May Have Low Accuracy in Younger Women

From Medscape Medical News
Laurie Barclay, MD

May 5, 2010 — Screening mammograms in younger women have low accuracy and detect few cancers, according to the results of a study published online May 3 in the Journal of the National Cancer Institute.

"Few data have been published on mammography performance in women who are younger than 40 years," write Bonnie C. Yankaskas, PhD, from the University of North Carolina at Chapel Hill, and colleagues. "We pooled data from six mammography registries across the United States from the Breast Cancer Surveillance Consortium."

The study cohort consisted of 117,738 women who had their first screening or diagnostic mammogram during 1995 to 2005, when they were 18 to 39 years of age. Follow-up for 1 year allowed the investigators to measure the accuracy of mammographic evaluation, recall rate for screening examinations, and sensitivity, specificity, positive predictive value, and cancer detection rate for all mammograms.

No cancers were detected in 637 screening mammograms performed in women 18 to 24 years of age. The largest number of screening mammograms in this study was in women aged 35 to 39 years (n = 73,335). In this group, the recall rate was 12.7% (95% confidence interval [CI], 12.4% - 12.9%), sensitivity was 76.1% (95% CI, 69.2% - 82.6%), specificity was 87.5% (95% CI, 87.2% - 87.7%), positive predictive value was 1.3% (95% CI, 1.1% - 1.5%), and cancer detection rate was 1.6 cancers per 1000 mammograms (95% CI, 1.3 - 1.9 cancers per 1000 mammograms).

Of the 86,871 women screened, 67,468 (77.7%) reported no family history of breast cancer. Across all age groups, the age-adjusted rates for diagnostic mammograms were sensitivity of 85.7% (95% CI, 82.7% - 88.7%), specificity of 88.8% (95% CI, 88.4% - 89.1%), positive predictive value of 14.6% (95% CI, 13.3% - 15.8%), and cancer detection rate of 14.3 cancers per 1000 mammograms (95% CI, 13.0 - 15.7 cancers per 1000 mammograms). Except for specificity, diagnostic measures of mammography performance were better in women who had a breast lump.

"Younger women have very low breast cancer rates but after mammography experience high recall rates, high rates of additional imaging, and low cancer detection rates," the study authors write. "We found no cancers in women younger than 25 years and poor performance for the large group of women aged 35-39 years. In a theoretical population of 10 000 women aged 35-39 years, 1266 women who are screened will receive further workup, with 16 cancers detected and 1250 women receiving a false-positive result."

Limitations of this study include a substantial amount of missing data and the inability to collect a complete family pedigree or BRCA1 or BRCA2 status, which would help identify women at very high risk.

The journal editors note that screening young women is not without potential harms, which may include additional radiation exposure, anxiety because of false-positive findings, and costs of additional imaging.

In an accompanying editorial, Ned Calonge, MD, MPH, from the Colorado Department of Public Health and Environment, Denver, calls this a "landmark descriptive study." He also points out that even women who had a family history of breast cancer had the same detection and false-positive rates as women without known family history, casting doubt on the recommendation of some health groups for early screening of women with a positive family history.

"[W]e must continue to strive for better tests and better treatments," Dr. Calonge writes. "We need clinical trial data on the screening utility of any modality or strategy for high-risk women in this age group and better data on the use of early or other enhanced screening for women with high-risk genetic mutations. Furthermore, we should not be satisfied with better detection rates alone: We need evidence that early detection of these cancers translates to improvements in important health outcomes. "

The National Cancer Institute–funded Breast Cancer Surveillance Consortium supported this study. Financial relationships for the authors were not reported in the study.

J Natl Cancer Inst. Published online May 3, 2010.