Detection of Bilateral Breast Cancer at Biennial Screening Mammography in the Netherlands: A Population-based Study

Purpose: To determine the incidence of bilateral breast cancer at biennial screening mammography and to assess the sensitivity of screening in the detection of bilateral breast cancer. Materials and Methods: All women gave written informed consent, and the requirement to obtain review board approval was waived. The authors included all 302 196 screening mammograms obtained in 80 466 women aged 50-75 years in a southern breast screening region of the Netherlands between May 1998 and July 2008. During 2-year follow-up, the authors collected clinical data, breast imaging reports, biopsy results, and breast surgery reports from all patients with screening-detected and interval cancers. Two screening radiologists reviewed the screening and clinical mammograms of all bilateral screening-detected and interval cancers for mammographic abnormalities. The radiologists were initially blinded to each other's referral opinion, and discrepant assessments were followed by consensus reading. Results: Of all women with screening-detected cancer (n = 1555) or interval cancer (n = 585), 52 (2.4%) had bilateral breast cancer. The sensitivity of screening mammography in the detection of bilateral breast cancer was 19% (10 of 52 women; 95% confidence interval: 8.5%, 29.9%). At blinded review, 18 of the 53 tumors not detected at screening (34%) were considered to be missed, 11 (21%) showed nonspecific minimal signs, and 24 (45%) had been mammographically occult at screening. Five women referred for further analysis experienced a 6-17-month delay in the diagnosis of the second breast cancer; in four of those women, the delay resulted from an incorrect Breast Imaging Reporting and Data System classification at clinical mammography. Conclusion: The sensitivity of screening mammography in the detection of bilateral breast cancer is disappointingly low. Both screening radiologists and clinical radiologists should pay vigorous attention to the contralateral breast to detect bilateral malignancies without diagnostic delay.