Do all patients with bilateral testis cancer have a hereditary predisposition?

An international study has demonstrated that patients with bilateral testicular cancer are significantly more likely to have brothers with testis cancer than those with unilateral disease. This, together with other evidence, implies that patients with bilateral disease are likely to carry a predisposing genotype. But is it the great majority of them which is thus predisposed? We show that if as few as half of these patients have the predisposing genotype, its penetrance would have to be 80%, causing 38% of resulting cases to be bilateral. Evidence from the International Testis Cancer Linkage Consortium shows that the proportion of familial cases with bilateral disease is much lower. It is likely that at least the majority of cases of bilateral testis cancer arise as a result of a predisposing genotype.