PD-L1 expression, molecular alterations and histopathological correlation in salivary gland adenoid cystic carcinomas

Amini F, PD-L1 expression, molecular alterations and histopathological correlation in salivary gland adenoid cystic carcinomas, Hacettepe University Faculty of Medicine, Pathology Thesis, Ankara, 2021. Adenoid cystic carcinomas (ACC) are one of the most destructive and unpredictable salivary gland tumors. MYB/MYBL1-NFIB translocations have been identified in these tumors. As a powerful diagnostic and prognostic tools, they also show promise as targets of therapy. Recent studies have reported that PD-L1 expression is associated with poor prognosis in many different malignancies, such as melanoma, non-small-cell lung carcinoma and renal-cell carcinoma. In these tumors, programmed death-1 (PD-1) targeted immunotherapies have shown significant clinical responses. There are few studies on PD-L1 expression in salivary gland tumors and research on clinicopathological behavior is ongoing. We thus aimed to investigate MYB/MYBL1-NFIB translocation and immunhistochemical PD-L1 expression status in salivary gland ACC from our archive and describe their clinical and histopathologic features. Fifty-six primary salivary gland ACC cases, 10 distant metastases and 6 lymph node metastasis foci which were diagnosed between 2000-2020 were included in this study. Sections obtained from formalin fixed paraffin embedded blocks have been used and immunohistochemical study for PD-L1 was performed. Since the different morphological features are likely to be associated with different fusion gene partners, different patterns of primary tumors were included in the molecular study separately and MYB/MYBL1-NFIB gene fusion was examined. In addition, molecular studies were applied to metastatic foci. As a result, twelve patients had MYB/MYBL1-NFIB translocations. Compatibility was observed between primary and distant metastasis foci in fusion-positive patients. It was observed that in the same patient, the molecular profiles of different morphological patterns may differ from each other. MYB fusion positive ACC cases were significantly older. PD-L1 expression generally was low and its positivity was significantly more frequent in elderly patients.