ERBB2 and rhabdomyosarcoma: All male mice develop rhabdomyosarcoma in the genitourinary tract around 4 months of age, with remarkable gender specificity (only males, not females, are affected by rhabdomyosarcoma), anatomic specificity (only urethral striated muscle proximal to the urinary bladder gives rise to tumors) and genetic specificity (urethral rhabdomyosarcoma only affects bigenic mice, but not parental mice carrying either a p53 inactivated allele or a HER-2/neu mutant allele).