A study including 1355 patients with all molecular subtypes found that IDC grade and Ki67 level were significantly lower in patients with DCIS components in IDC disease.8 Another study conducted in ER-positive patients discovered that concomitant DCIS was associated with smaller tumours and less node involvement.7 Similar to these studies, our study found that the DCIS component in IDC was more common in younger patients and was significantly correlated with lower IDC grade. This evidence concerns the gene MKI67 and ductal breast carcinoma in situ.