In normal lobules, DDR1 is expressed in the cytoplasm and membranes of normal epithelial cells. No DDR1 staining is observed in the stromal fibroblasts. DDR2 is not detectable in normal lobules. In DCIS, DDR1 is expressed in the cytoplasm and membrane of cancer cells. DDR2 is expressed focally in groups of cells at the periphery of the ducts (black arrows). The cancer cells located in the center of the DCIS are negative for DDR2. Inset shows specific cytoplasmic staining for DDR2 in DCIS cells adjacent to the stroma (asterisk). Note that the stromal fibroblasts also express DDR2 in the cytoplasm (asterisk). Representative invasive ductal carcinomas with different levels of DDR expression. Tumor 1 exhibits high DDR1 and low DDR2, Tumor 2 exhibits low DDR1 and high DDR2, and Tumor 3 has high expression of DDR1 and DDR2. Magnification 400x, insets 600x.