Frequency and survival of delayed breast cancer diagnosis in women participating at screening mammography in the Netherlands: a population-based study.

Background: Although breast cancer screening programmes aim to enable early breast cancer detection, diagnostic delays still occur among participants. Limited information is available on the frequency and survival of women with a delay in breast cancer diagnosis within the screening population. We determined the frequency of various types of delay in breast cancer diagnosis at screening mammography and specified the tumour characteristics, surgical therapy and survival rates of women with these delayed diagnoses, as well as variations in their proportions over time. Methods: We included 901,133 screening examinations obtained in the southern Netherlands between 1999 and 2019. Screening mammograms of women with interval cancers (ICs) and breast cancers detected at subsequent screening were reviewed to determine whether the cancer had been missed. Findings: Of the 7129 women with breast cancers, 5419 (76.0%) were diagnosed without delay after recall and 1101 (15.4%) had a true IC (i.e., not detectable at the previous screen). In total, 1601 women experienced a delay in breast cancer diagnosis, comprising the following three study groups: (i) recalled women with a delay in diagnostic work-up (n = 264), (ii) recalled women with screen-detected cancers (SDCs) at subsequent screening and without a delay in diagnostic work-up, that had been missed at the previous screening round (n = 992), and (iii) women with ICs missed at the latest screening round (n = 345). Overall, 26.6% of cancers were associated with a delay (1601/6028), primarily due to SDCs missed at the previous screen (62.0%, 992/1601), followed by missed ICs (21.5%, 345/1601) and misdiagnosis after recall (16.5%, 264/1601). Compared to SDCs missed at the previous screen and misdiagnosis after recall, missed ICs demonstrated the poorest tumour characteristics, highest mastectomy rate (42.6% vs 20.1% and 19.3%, p < 0.0001) and poorest overall survival (5-year rate 86.9% vs 93.8% and 93.8%, p = 0.0017). Temporal trends in tumour characteristics were mainly observed in SDCs missed at the previous screen. Interpretation: Delayed breast cancer diagnosis at screening mammography or after recall remains a serious point of concern. Most delays are related to SDCs missed at a previous screen, whereas missed ICs show the worst survival. Funding: This research did not receive any funding.