The reasons for not identifying one in all four patients, could be due to e.g. possible variations in monoclonal versus polyclonal origins of the metastasis, as previously described.5,7,47 Additional variation in transcriptional profiles within the likely seeding focus could introduce another source of noise, as exemplified by Suh et al.,48 reporting intrafocal heterogeneity of ERG protein expression and gene fusion patterns in PC. The gene discussed is ERG; the disease is pachyonychia congenita.