Four clones with strong ELISA signals (P4G9, P3A7, P3D2, P3G4) stained fixed cells of four cell lines (MCF-7, nontumorigenic breast; MB-231, tumorigenic breast cancer; HTB-66, tumorigenic melanoma; U87, tumorigenic glioblastoma), demonstrating that the cells of all four cell lines expressed the CD44 target antigen (Fig 2B). The gene discussed is CD44; the disease is breast cancer.