Homeodomain-only protein is located in a chromosomal region (4q11–q12) that is frequently deleted in solid tumours, including lung tumours, hepatocellular carcinoma and bladder cancer (Petersen et al, 1997; Koo et al, 1999; Sakakura et al, 1999; Wong et al, 1999). The gene discussed is HOPX; the disease is urinary bladder carcinoma.