Advancing Education, Research, and Quality of Care for the Head and Neck oncology patient.
Introduction: Salivary adenoid cystic carcinoma (sAdCC) is a rare, slow-growing head and neck tumor. Compared to other head and neck sites, submandibular gland sAdCCs exhibit different behavior in terms of prognosis. However, the molecular differences between subtypes, and the tumor immune microenvironment (TIME) differences are unclear.
Materials and methods: A pooled-cohort of previously published RNA sequencing datasets, (27 sAdCC and 21 controls), and validation RNA sequencing dataset of 33 minor gland sAdCCs were used. A clinically annotated, in-house cohort of 39 samples (30 sAdCC and 9 controls) was also generated. Single sample gene set enrichment analysis (ssGSEA) and TIME deconvolution were performed on the RNA sequencing data. Additionally, quantitative PCR (qPCR), multiplex immunofluorescence (mIF) and RNA seq were performed on the in-house cohort to further investigate site-specific differences. Statistical analysis included Wilcoxon rank-sum, nonparametric equality-of-medians tests and linear regression models.
Results: sAdCC expression of tumorigenic pathways varies by anatomic subsite, with the reactive oxygen species (ROS)/NRF2 pathway signature being significantly under-expressed in submandibular gland sAdCCs compared to other head and neck sites. Further, NRF2-pathway which was overexpressed in parotid gland sAdCCs, was also positively associated with overall survival (OS). In TIME, CD4+ T cell population differences were identified between major and minor gland sAdCC, and natural killer (NK) cell concentration was different between minor, submandibular and parotid gland sAdCCs. Additionally, while plasma cell population differences were not detected in sAdCCs, normal submandibular glands were more enriched than other normal gland controls.
Conclusions: Our data investigate for the first time the molecular background of survival and treatment response differences observed between patients with sAdCC located in different head and neck locations. Specifically, the ROS/NRF2 pathway appears to be a major driver of survival differences. High ROS levels in sAdCC cells have previously been associated with decreased clonogenicity and higher autophagy. NRF2 pathway activation could be a result of the increased ROS levels in these tumors, explaining the improved survival of parotid sAdCC patients. CD4+ T, NK cell, and plasma cell populations are also different across gland types, suggesting that the tumor-intrinsic pathway differences observed in the submandibular sAdCC may affect TIME composition.