It is worth noting that neither of these markers conclusively confirms the identity of PPGL tumour cells, but based on the widespread staining of early cultures and the general co-occurrence of synaptophysin and tyrosine hydroxylase-positive cells in cultures exhibiting long-term survival of putative tumour cells, together with a consistent cell morphology, we conclude with a considerable degree of confidence that these cells are genuine, persistent chromaffin tumour cells. This evidence concerns the gene SYP and neoplasm.