Immunohistochemical Expression of CD₅₆ and ALDH₁ in Common Salivary Gland Tumors

Natural killer (NK) cells, of which CD₅₆ is a specific marker, play an important role in host defense against tumors. Cancer stem cells, of which aldehyde dehydrogenase isoform 1 (ALDH₁) is an immunohistochemical marker, are a group of tumorigenic cells which are involved in migration and tumor recurrences. We aimed to evaluate the expression of ALDH₁ and CD₅₆ in common salivary gland tumors, as well as their relationship with each other and with a number of clinicopathologic factors.

Forty-five paraffin blocks of salivary gland tumors (pleomorphic adenoma, mucoepidermoid carcinoma and adenoid cystic carcinoma, 15 samples each) were selected. Malignant tumors were classified into two groups: low-grade (including mucoepidermoid carcinoma grade I) and high-grade (including mucoepidermoid carcinoma grade III and adenoid cystic carcinoma). Immunohistochemical staining for ALDH₁ and CD₅₆ markers was performed. Data were analyzed using SPSS (20) and the Chi-square test.

CD₅₆ expression was significantly higher in benign and high-grade malignant tumors (P=0.01). ALDH₁ overexpressed in all three salivary tumors, but not to statistically significant degree (P=0.54). There was no statistically significant correlation between ALDH₁ and CD₅₆ expression with demographic factors (age, gender, or location of tumor; P>0.05).

It appears that the number of NK cells and their function change in different types of salivary gland tumors (benign/malignant) and stroma. NK cells are important components of the anti-tumor system; therefore immune dysfunction is associated with tumor progression in tumors of the salivary gland. ALDH₁ overexpression suggests its role in tumorogenesis, but ALDH₁ is not involved in the morphogenesis of salivary gland tumors.