Evaluation and characterization of the extracellular matrix in salivary gland tumors through histochemistry and second harmonic generation

Abstract

Objective

To describe extracellular matrix (ECM) components in salivary gland tumors with and without myoepithelial differentiation.

Design

Five cases of each tumor type were analyzed: pleomorphic adenoma, myoepithelioma, adenoid cystic carcinoma, myoepithelial carcinoma, epithelial-myoepithelial carcinoma, and salivary duct carcinoma. Histochemical stains identified collagen fibers, elastin, proteoglycans (PG), and glycosaminoglycans (GAG). Collagen was further examined by second harmonic generation (SHG) in three regions: tumor stroma, extratumoral stroma, and capsule. ImageJ was used to analyze area fraction, mean gray level, entropy, and contrast. Data underwent statistical analysis (p < 0.0001).

Results

ECM composition varied among salivary gland tumors. Pleomorphic adenoma showed low elastin and collagen, but PG and GAG were present in over 50 % of cases. Myoepithelioma showed variable collagen and elastin, while adenoid cystic carcinoma had predominant collagen. Myoepithelial carcinoma presented inconsistent elastin and low collagen. Epithelial-myoepithelial carcinoma and salivary duct carcinoma showed intense collagen staining. SHG revealed higher area fraction and gray level in the extratumoral region. Entropy was significantly higher outside the tumor. Malignant tumors with myoepithelial differentiation showed increased values in all SHG parameters compared to benign counterparts.

Conclusions

Benign tumors expressed more PG and GAG, whereas malignant ones had increased collagen with structural alterations. SHG analysis indicated lower collagen intensity within tumors and highlighted the role of ECM remodeling in malignancy, invasion, and metastasis.