Abstract
ObjectiveTo perform a radiological review of mammograms from prior screening and diagnosis of screen-detected breast cancer in BreastScreen Norway, a population-based screening program.MethodsWe performed a consensus-based informed review of mammograms from prior screening and diagnosis for screen-detected breast cancers. Mammographic density and findings on screening and diagnostic mammograms were classified according to the Breast Imaging-Reporting and Data System®. Cases were classified based on visible findings on prior screening mammograms as true (no findings), missed (obvious findings), minimal signs (minor/non-specific findings), or occult (no findings at diagnosis). Histopathologic tumor characteristics were extracted from the Cancer Registry of Norway. The Bonferroni correction was used to adjust for multiple testing; p < 0.001 was considered statistically significant.ResultsThe study included mammograms for 1225 women with screen-detected breast cancer. Mean age was 62 years ± 5 (SD); 46% (567/1225) were classified as true, 22% (266/1225) as missed, and 32% (392/1225) as minimal signs. No difference in mammographic density was observed between the classification categories. At diagnosis, 59% (336/567) of true and 70% (185/266) of missed cancers were classified as masses (p = 0.004). The percentage of histological grade 3 cancers was higher for true (30% (138/469)) than for missed (14% (33/234)) cancers (p < 0.001). Estrogen receptor positivity was observed in 86% (387/469) of true and 95% (215/234) of missed (p < 0.001) cancers.ConclusionsWe classified 22% of the screen-detected cancers as missed based on a review of prior screening mammograms with diagnostic images available. One main goal of the study was quality improvement of radiologists’ performance and the program. Visible findings on prior screening mammograms were not necessarily indicative of screening failure.Key Points• After a consensus-based informed review, 46% of screen-detected breast cancers were classified as true, 22% as missed, and 32% as minimal signs.• Less favorable prognostic and predictive tumor characteristics were observed in true screen-detected breast cancer compared with missed.• The most frequent mammographic finding for all classification categories at the time of diagnosis was mass, while the most frequent mammographic finding on prior screening mammograms was a mass for missed cancers and asymmetry for minimal signs.
Highlights
Breast cancer is diagnosed among screening participants as screen-detected breast cancer or interval breast cancer
Breast cancer can be missed at screening due to misperception—the lesion is not perceived by the radiologist—or misinterpretation—the lesion is detected by the radiologist, but not considered suspicious enough to warrant a recall, either by the reading radiologist or at a consensus meeting
The study was approved by the data protection official at the Cancer Registry of Norway (CRN) (PVO approval number: 2016/4696), and the local breast centers agreed to the study
Summary
Breast cancer is diagnosed among screening participants as screen-detected breast cancer or interval breast cancer (breast cancer diagnosed between two scheduled screening rounds after a negative screening episode). When obvious mammographic findings corresponding to the location of the tumor are visible on prior screening mammograms, which in retrospect should have resulted in a recall, the cancer may be defined as missed. Up to 50% of interval and screen-detected breast cancers can present visible findings on prior screening mammograms, ranging from minor benign-looking findings to obviously missed cancers [1,2,3,4,5,6,7,8]. Breast cancer can be missed at screening due to misperception—the lesion is not perceived by the radiologist—or misinterpretation—the lesion is detected by the radiologist, but not considered suspicious enough to warrant a recall, either by the reading radiologist or at a consensus meeting. Mammographic density may impact the rates of missed breast cancer due to the masking effect of dense breast tissue and overlapping structures [11]
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