Objective Parotid tumors are rare neoplasms in adults but are exceedingly infrequent in adolescents. We aimed to determine the clinical characteristics and outcomes of parotid tumors in adolescents under 20 years old. Methods Between 1999 and 2020, 979 cases of benign parotid tumors and 236 cases of malignant parotid tumors were treated surgically in our department. Of these, 12 benign cases (1.2%) and 9 malignant cases (3.8%) were in adolescents. There were no benign or malignant cases for those aged under 10 years. Results Regarding the histological type, all benign tumors were pleomorphic adenomas. About half of malignant tumors were mucoepidermoid carcinomas, and excluding one high-grade case, the grade of malignancy was all low/intermediate. The accuracy of fine-needle aspiration cytology among adolescents showed no significant difference with that of adults. In contrast to adults, adolescent benign tumor cases showed a markedly high rate of pleomorphic adenomas and no postoperative facial nerve palsy. Malignant tumors in adolescents had a different trend than adults; low/intermediate-grade malignancies were common and thus few symptoms/signs of malignancy could be observed. As well, the accuracy of fine-needle aspiration cytology was poor. All cases had a good prognosis and are disease-free survival. Conclusion Parotid tumors in adolescents are rare but have several characteristics that are distinct from adults. As long-term observation is required posttreatment in adolescent patients, recurrence in benign pleomorphic adenomas and poor long-term prognosis in malignant tumors, especially for those with low/intermediate-grade malignancy, are more likely to be observed.

Background Parotid cancer is relatively rare, and malignancy varies; therefore, novel markers are needed to predict prognosis. Recent advances in matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), useful for visualization of lipid molecules, have revealed the relationship between cancer and lipid metabolism, indicating the potential of lipids as biomarkers. However, the distribution and importance of phospholipids in parotid cancer remain unclear. Objective This study aimed to use MALDI-IMS to comprehensively investigate the spatial distribution of phospholipids characteristically expressed in human parotid cancer tissues. Methods Tissue samples were surgically collected from two patients with parotid cancer (acinic cell carcinoma and mucoepidermoid carcinoma). Frozen sections of the samples were assessed using MALDI-IMS in both positive and negative ion modes, with an m/z range of 600–1000. The mass spectra obtained in the tumor and non-tumor regions were compared and analyzed. Ion images corresponding to the peak characteristics of the tumor regions were visualized. Results Several candidate phospholipids with significantly different expression levels were detected between the tumor and non-tumor regions. The number of unique lipid peaks with significantly different intensities between the tumor and non-tumor regions was 95 and 85 for Cases 1 and 2, respectively, in positive ion mode, and 99 and 97 for Cases 1 and 2, respectively, in negative ion mode. Imaging differentiated the characteristics that phospholipids were heterogeneously distributed in the tumor regions. Conclusion Phospholipid candidates that are characteristically expressed in human parotid cancer tissues were found, demonstrating the localization of their expression. These findings are notable for further investigation of alterations in lipid metabolism of parotid cancer and may have potential for the development of phospholipids as biomarkers.

Objectives CD81, a transmembrane protein belonging to the tetraspanin family, has recently attracted attention as a therapeutic target for cancer owing to its important role in human cancer biology; however, there is no previous knowledge regarding CD81 expression in parotid cancer. Therefore, this study aimed to investigate CD81 expression in human parotid cancer and its involvement in cell proliferation. Materials and Methods Tissue samples were collected from 36 patients with parotid cancer, including 10 with salivary duct carcinoma (SDC), 16 with mucoepidermoid carcinoma (MEC), 5 with adenoid cystic carcinoma (ACC), and 5 with carcinoma ex pleomorphic adenoma (Ca ex PA). CD81 expressions in parotid cancer tissues were evaluated using western blotting and immunohistochemistry. Parotid cancer cell lines were established and the effect of suppressing CD81 expression by small interfering RNA (siRNA) and the effect of our anti-CD81 monoclonal antibody on the growth of parotid cancer cells were evaluated. Results The immunohistochemical expressions of CD81 on tumor cell membranes were observed in SDC and MEC tissues but not in ACC and Ca ex PA tissues. Furthermore, inhibition of CD81 expression by siRNA suppresses the growth of parotid cancer cells, and the mouse monoclonal antibody against CD81 inhibited parotid cancer cell growth in a concentration-dependent manner. Conclusions We confirmed the expressions of CD81 in SDC and MEC tissues and showed that its inhibition suppressed the growth of parotid cancer cells. Clinical Relevance These findings provide primary data for the therapeutic targeting of CD81 in parotid cancer.

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