Treatment of Ductal Carcinoma in situ: A Register-Based Study of Norwegian Women Diagnosed between 1995 and 2018

INTRODUCTION: The incidence of ductal carcinoma in situ (DCIS) has increased after implementation of mammographic screening. The lesion represents management challenges due to its undetermined growth pattern. We aimed to explore treatment of women aged 48–71 years diagnosed with DCIS between 1995 and 2018, by detection mode and histopathological characteristics. MATERIAL AND METHODS: Data on surgical treatment and radiation therapy (RT) of 4,995 women diagnosed with DCIS were retrieved from the Cancer Registry of Norway. We described the percentage and frequency of breast-conserving treatment (BCT) for participants in BreastScreen Norway (screen-detected) and nonparticipants. We estimated the relative risk (RR) of BCT, using log-binomial regression models. RESULTS: Use of BCT increased from about 40% in 1995 to 85% in 2018. Use of BCT was more common among older than younger women and more commonly used for screen-detected versus tumors detected outside the screening program. Nine out of ten women with tumors ≤10 mm were treated with BCT and two out of ten with tumors >50 mm. RT was given to 89.3% of the women with tumors ≤10 mm, 34.1% of those with tumors classified as van Nuys' grade 1 and <10 mm and 96.0% of the tumors >50 mm. Use of BCT was less common for tumors >50 mm compared to <10 mm (RR adjusted for age, detection mode, van Nuys' grade, and localization: 0.26, 95% CI: 0.19–0.36). CONCLUSION: BCT was increasingly used among women diagnosed with DCIS in Norway during the period from 1995 to 2018, particularly for screen-detected, small lesions with low van Nuys' grade.