Infiltrating ductal carcinoma (IDC) occurs frequently in patients with lobular carcinoma in-situ (LCIS). LCIS is not thought to be the direct precursor of the invasive component. The authors analyzed 15 cases of coexisting LCIS and IDC and found ductal carcinoma in situ (DCIS) in 12. The DCIS and IDC were of similar grade and located in the same area. Selected cases stained with E-cadherin demonstrated a different immunophenotype for the lobular and ductal lesions. These results support the notion that DCIS is the direct precursor of IDC occurring in patients with LCIS.