Multiparameter DNA flow-sorting demonstrates diploidy and SDHD wild-type gene retention in the sustentacular cell compartment of head and neck paragangliomas: chief cells are the only neoplastic component.

Head and neck paragangliomas are considered to be biphasic tumours, composed of two distinct cell types: chief cells and sustentacular cells. A substantial number of these tumours show mutations in the SDHD gene located at chromosome 11q23. Although there is general agreement that paragangliomas are a neoplastic proliferation of chief cells, the nature of sustentacular cells is still a matter of debate. To clarify the nature of sustentacular cells further, multiparameter DNA flow cytometry was performed utilizing S-100 labelling as a selective marker of the sustentacular fraction simultaneously with DNA content measurement in six head and neck paragangliomas. S-100-positive fractions and other tumour-cell populations were flow-sorted and restriction digestion analysis of SDHD mutations was performed on each fraction. Flow cytometry demonstrated that the S-100 labelled cells were diploid. Restriction digestion analysis in informative cases revealed retention of the wild-type SDHD allele in S-100-positive fractions and loss of the wild-type allele in S-100-negative fractions. These data strongly suggest that sustentacular cells should be regarded as a non-neoplastic cell population that may be induced as a tumour-specific stromal component by chief cells.