TMPRSS2-ERG, the abnormal fusion between a transmembrane serine 2 protease gene (TMPRSS2) and E26 oncogene homolog (ERG) gena protease, has been found to occur with high frequency in PC since the early stages of disease; it has a high specificity of 93% and PPV of 94% for PC diagnosis in the prebiopsy setting [44]. The gene discussed is TMPRSS2; the disease is pachyonychia congenita.