Risk of breast cancer by prior screening results among women participating in BreastScreen Norway

Background A premalignant lesion in the breast is associated with an increased risk of breast cancer. The aim of this article was to identify women with an increased risk of breast cancer based on prior screening results (PSRs). Methods This registry‐based cohort study followed women who participated in the organized breast cancer screening program in Norway, BreastScreen Norway, in 1995‐2016. Incidence rates and incidence rate ratios were used to estimate absolute and relative risks of breast cancer associated with PSRs. Histopathological characteristics of subsequent breast cancers were presented by PSRs. Results This study included 762,643 women with up to 21 years of follow‐up. In comparison with negatively screened women, increased incidence rate ratios of 1.8, 2.0, 2.9, and 3.8 were observed after negative additional imaging, for benign biopsy, for hyperplasia with atypia, and for carcinoma in situ, respectively. Subsequent breast cancers did not differ in tumor diameter or histological grade, whereas the proportion of lymph node–positive breast cancers decreased as the presumed malignancy potential of PSRs increased. Conclusions The risk of subsequent breast cancer increased with the presumed malignancy potential of PSRs, whereas the tumor characteristics of subsequent cancers did not differ except for the lymph node status. Women with screen‐detected benign lesions or hyperplasia with atypia might benefit from more frequent screening. The long‐term risk of breast cancer is estimated from the results of prior screening examinations. The observed (absolute and relative) risk of breast cancer increases with the presumed malignancy potential of prior screening results, including the histopathological type of the lesions.