In PC-15, a patient with treatment emergent small-cell neuroendocrine PC, CTCs expressing neuroendocrine markers (SYP, CHGA, NCAM1) and DLL3 co-occurred with elevated blood levels of neuron-specific enolase (1451 ng/ml) and chromogranin A (2764 ng/ml). This evidence concerns the gene ENO2 and pachyonychia congenita.