Comparing “pure” DCIS with mixed-type DCIS lesions revealed significantly lower protein levels of KRT5, KRT14, KRT6B, and CEACAM5 in “pure” DCIS lesions (P < 0.05; see Supplementary Table S3), indicating stromal remodeling as a key feature in the progression from precancer to invasive cancer, with prognostic value for DCIS management. Here, KRT5 is linked to ductal breast carcinoma in situ.