Primary tumour cells were isolated from breast tissue of a patient with an infiltrating ductal carcinoma (IDC) and with the following histologic features: moderately differentiated, G2, pT2, pN1a, MIB-1 (KI-67) proliferation index 21%, ER+/PR+, HER2-. This evidence concerns the gene MKI67 and invasive ductal breast carcinoma.