Despite population screening, a high prevalence of breast cancer following a normal screening mammogram was observed from results of a registry-based cohort study, which were published in JAMA Network Open.

Data from 69,025 women aged 50 to 64 years included in 3 datasets collected between 2004 and 2010 in Canada were combined for this study. Information on breast cancer and long-term prognoses were analyzed. Interval cancers were defined as a breast cancer diagnosed within 24 months of a normal screening mammogram and noncompliance was designated when a breast cancer diagnosis occurred more than 2 years after a previous mammography.

The included women had a total of 212,579 mammograms and 1687 cases of invasive breast cancer. Among cancers, 705 were screen-detected, 501 were detected outside of the screening program, 275 were among noncompliant women, and 206 were interval cancers.

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At a median follow-up of 7 years, 170 women had died from their breast cancer. Of these women, 94 were detected outside of screening programs, 29 had been interval cancers, 27 had been noncompliant, and 20 had been screen-detected. Mortality risk was higher among women with interval cancers compared against women with screen-detected cancers (hazard ratio [HR], 5.44; 95% CI, 3.08-9.60; P <.001).

A limitation of this study was that the investigators did not adjust for length time bias, possibly exaggerating the survival benefit.

These data indicated that substantial inadequacies exist in current breast cancer screening programs in Canada, in which lethal cancers were missed during examination or that screening intervals were insufficient to detect lethal cancers among patients.

Disclosures: One author declared affiliation with industry. Please refer to the original article for a full list of disclosures.


Niraula S, Biswanger N, Hu P, Lambert P, Decker K. Incidence, characteristics, and outcomes of interval breast cancers compared with screening-detected breast cancers. JAMA Netw Open. 2020;3(9):e2018179. doi:10.1001/jamanetworkopen.2020.18179