Pleomorphic adenomas are the most common salivary gland tumour. Although this tumour is considered to be of epithelial origin, it contains 'mesenchyme'-like elements histologically.
Lumican is a keratan sulphate
proteoglycan that belongs to the small
leucine-rich repeat (LRR)
proteoglycans and has been reported to be associated with cartilage formation. These findings suggest that
lumican expression may be related to the chondroid component in
pleomorphic adenomas. To investigate this hypothesis, the present study investigated the expression and localization of
lumican in 20 normal human salivary glands and 35
pleomorphic adenomas. Firstly, immunohistochemistry for
lumican was performed with
pepsin pretreatment. In normal salivary glands,
lumican was deposited in the periductal regions. In
pleomorphic adenomas, it was predominantly deposited in the hyaline (100%) and fibrous areas (89.4%). In 16 tumours (66.7%),
lumican was also deposited in the chondroid areas. Without
pepsin pretreatment,
lumican was identified in myoepithelial cells in myxoid areas, lacuna cells in chondroid areas, and in the cytoplasm of inner ductal cells. In situ hybridization revealed
lumican mRNA expression mainly in the inner cells, the neoplastic myoepithelial cells, and the lacuna cells. These results suggest that
lumican is associated with the formation of 'mesenchyme'-like structures in
pleomorphic adenomas. In conclusion, normal salivary glands express
lumican, which appears to be related to stromal maintenance, and
pleomorphic adenomas express
lumican mRNA and
protein, which may play important roles in the formation of 'mesenchyme'-like areas in this type of tumour.