To investigate the hypothesis that comedo-ductal carcinoma in situ (DCIS) serves as a potential precursor entity for basal-like breast cancers, we analyzed expression of p63, CK5, Her2, EGFR, ER and PgR in clinical comedo- and noncomedo-DCIS and the MCF10DCIS.com xenograft model of human comedo-DCIS. The gene discussed is ESR1; the disease is ductal breast carcinoma in situ.