Risk of subsequent invasive breast carcinoma after in situ breast carcinoma in a population covered by national mammographic screening

Abstract

Sweden was the first country to establish a nationwide breast cancer screening service. We used the Swedish Family-Cancer Database to evaluate the risk of invasive carcinoma after in situ carcinoma of the breast. Risk estimates for contralateral and ipsilateral invasive malignancies following age and histology specific in situ breast carcinomas were calculated using Poisson's regression analysis. The agreement between concordant and discordant morphologies of invasive and in situ breast cancer was measured using the kappa statistic. Women with in situ breast cancer showed a relative risk of 2.03 for contralateral and 3.94 for ipsilateral invasive breast cancer. The risk was higher for in situ carcinomas diagnosed before the age of 50 years and after lobular in situ breast cancers. A comparison of the risks during the past decades suggested that the risk of ipsilateral breast cancer has increased in Sweden but that of contralateral breast cancer has remained unchanged. In situ and the subsequent invasive breast cancers did not seem to share their morphologies.