Screen-Detected Breast Cancer Outcomes by Mammography Participation in Immediate Past Screening.

Importance: Mammography screening is essential for the early detection of breast cancer; however, delayed detection among screen-detected breast cancers (SDBCs) is rarely studied. Objectives: To investigate whether women diagnosed with SDBC who missed the screening round immediately before the diagnostic round experience clinically significant delays in detection and whether tumor characteristics vary. Design, Setting, and Participants: This prospective register-based cohort study included all women diagnosed with SDBC in Stockholm, Sweden, between January 1, 1995, and February 28, 2020, with a follow-up until December 31, 2022. Data were analyzed from November 5, 2023, to May 27, 2024. Exposure: Nonparticipation in the screening immediately prior to the diagnostic round. Main Outcomes and Measures: Tumor characteristics and breast cancer-specific survival. Results: Among 8602 women with SDBC (median age at diagnosis, 61 [IQR, 55-66] years), 1482 (17.2%) did not attend the immediate past screening. Nonparticipants in the past screening were more likely to have larger tumors (adjusted odds ratio [AOR], 1.55 [95% CI, 1.37-1.76] for a tumor size ≥20 mm), lymph node involvement (AOR, 1.28 [95% CI, 1.12-1.45), and distant metastasis (AOR, 4.64 [95% CI, 2.10-10.29]) and less likely to have estrogen receptor-negative breast cancer (AOR, 0.74 [95% CI, 0.60-0.92]); however, there were no differences in progesterone receptor status (AOR, 0.96 [95% CI, 0.83-1.11]) or ERBB2 (formerly HER2 or HER2/neu) status (AOR, 1.00 [95% CI, 0.81-1.24]). In addition, these women experienced poorer breast cancer-specific survival, with an adjusted hazard ratio (AHR) of 1.33 (95% CI, 1.08-1.65). There was no association after adjusting for tumor characteristics (AHR, 1.11 [95% CI, 0.89-1.38]). Additionally, no association was found between nonparticipation in the second-to-last screening and tumor characteristics among those with screen-detected breast cancers (AHR, 0.98 [95% CI, 0.80-1.19] for stage II tumors or higher). Conclusions and Relevance: The findings of this cohort study suggest that some women with SDBC experience delayed detection and have clinically relevant worse outcomes. Future research is needed to investigate whether advancing the next mammography screening invitation date could enhance early detection and improve breast cancer outcomes in this population.