MUC4 was expressed particularly in lung carcinomas (Copin et al, 2001) and, interestingly, it was proposed as a ligand for HER2 (Moniaux et al, 1999; Carraway et al, 2002), a growth factor receptor of the tyrosine kinase family, putatively implicated in hormonal escape of breast and prostate cancers. The gene discussed is MUC4; the disease is prostate carcinoma.