CD24 and CD44 in salivary gland pleomorphic adenoma and in human salivary gland morphogenesis: differential markers of glandular structure or stem cell indicators?

Aims Salivary gland neoplasms originate from salivary gland compartments, to which they are histologically related. Pleomorphic adenoma (PA) is a benign salivary gland neoplasm that comprises epithelial and myoepithelial cells and a complex stroma, whose structure, architecture and origin (from intercalated ducts) suggest stem cell participation. We compared the expression of CD24 and CD44 in PA and in developing human salivary glands to investigate whether these markers can be considered as cancer stem cell markers. Methods and results One hundred and one cases of PA and salivary gland specimens from 20 human fetuses were examined by immunohistochemistry and real-time reverse transcription polymerase chain reaction (RT-PCR). All PAs were positive for CD24 and CD44 by immunohistochemistry: neoplastic luminal structures were positive for CD24; modified myoepithelial cells were positive for CD44. In fetal salivary glands, these markers were restricted to the intercalated duct region. Real-time RT-PCR assays detected increased expression of CD44, but not CD24, in PA specimens in comparison with normal salivary gland controls. Conclusions PA and stem cells share the expression of CD24 and CD44; their value as markers of neoplastic cell multipotency and the implications of their expression for tumour behaviour are yet to be determined.