BACKGROUND: Incidence rates of ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) have been rising, but little is known about which patients will develop invasive breast cancer or what types of tumors these patients may develop. METHODS: By using Surveillance, Epidemiology and End Results (SEER) data, the authors evaluated how types of invasive breast cancers diagnosed among 37,692 DCIS and 4490 LCIS patients differed and how clinical characteristics influenced subsequent breast cancer risk. RESULTS: Among DCIS patients, incidence rates of ipsilateral and contralateral invasive breast cancer were 5.4/1000 person-years and 4.5/1000 person-years, respectively; and among LCIS patients, incidence rates were 7.3/1000 person-years and 5.2/1000 person-years, respectively. LCIS patients were 5.3-fold more likely than DCIS patients to develop invasive lobular carcinomas. Women whose DCIS had comedo histologic features or was poorly differentiated had 1.4-fold and 2.0-fold elevations in ipsilateral invasive breast cancer risk. Furthermore, among DCIS patients, 20-49 year-olds and black women and Hispanic white women had 1.6, 2.7, and 2.3-fold elevated risks of Stage III/IV breast cancer compared with 50-59 year-olds and non-Hispanic whites, respectively. CONCLUSIONS: Screening young DCIS patients more frequently and improving the follow-up care of blacks and Hispanic whites with DCIS may reduce their risk of advanced-stage breast cancer. In addition, LCIS may be a precursor rather than just an ambiguous risk factor for invasive breast cancer, and, therefore, localized treatment for LCIS may be warranted. Given that incidence rates of DCIS and LCIS have been rising, investigations of these tumors should be continued to better understand their etiology and appropriate clinical management.