CYB5R1 and neoplasm: Interestingly, while CYB5R1 marked most tumor cells in cases with strong expression by definition, cancers with weak or moderate CYB5R1 expression showed a distinct intratumoral distribution of this protein: In most of these tumors (83%), expression was pronounced at the infiltrative tumor edge, and was most strong in tumor cells that invaded the surrounding stroma by apparently detaching from the gland forming tumor mass (Figure 1).