SYP and neoplasm: It is worth remembering that neither synaptophysin nor tyrosine hydroxylase expression conclusively establishes the identity of a cell as a PPGL chromaffin tumour cell, but in light of the widespread staining in early cultures and the common co-occurrence of positive synaptophysin and tyrosine hydroxylase staining in cells of identical morphology, it is reasonable to assume that these cells are undifferentiated chromaffin tumour cells.