Testicular cancer is the most common cancer affecting young men and, like many other adult-onset cancers, multiple-case families do occur.  The genetic architecture of familial and sporadic cancers often differs, with rare, highly-penetrant mutations causing the former, and multiple common low-penetrance genetic variants underlying the latter. The study by Kratz and colleagues investigated familial testicular cancer and found that familial and sporadic testicular cancer share the same genetic architecture: both are associated with the same common genetic variants. This study has strong implications for genetic counseling, but does not exclude the existence of rare monogenic forms of familial testicular cancer. (By Christian P. Kratz, M.D., http://jmg.bmj.com/content/48/7/473 )