MKI67 and ductal breast carcinoma in situ: Basal-like breast cancers are considered the most aggressive subtype for IDC, but not for DCIS.2,4 Increased expression of biomarkers such as COX2, FOXA1, HER2, Ki-67, p16/INK4A, PR, and SIAH2 are associated with higher risk of recurrence for a subset of DCIS cases but do not predict invasiveness.2,5,6 By understanding the mechanisms that regulate DCIS progression, we may develop more effective treatments to reduce under- and over-treatment.