Immunohistochemical double-staining of human breast tumors for CD44 and CD24. CD44 is stained with Permanent Red and CD24 with diaminobenzidene (DAB). Magnification × 20. (a) A tumor positive for both CD44+/CD24- (white arrow) and CD44-/CD24+ (black arrow) cancer cells, although the predominant phenotype is CD44-/CD24-. (b) Almost all cells in this tumor are CD44+/CD24-. No CD24 staining is seen. (c) A tumor with predominantly CD44+/CD24- cells. A few CD44+/CD24+ cells are also present (black arrow). (d) A tumor positive for the CD44-/CD24+ phenotype. No CD44 staining is present.