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Background: Data relating to the efficacy of immune checkpoint inhibitors (ICI) for salivary gland carcinomas (SGC) is gradually evolving with responses varying among different histotypes. To address these disparities, this retrospective analysis examined the prevalence of recognized biomarkers of response to ICI; namely programmed death‐1 (PD‐1), programmed death‐ligand 1 (PD‐L1), combined positive score (CPS), epidermal growth factor receptor (EGFR), and microsatellite instability (MSI) in patients with SGC with an aim to determine any prognostic or survival benefits and stratify the use of ICI in this disease. Patients and methods: Of 52 patients with primary SGC eligible for this study, the most common histological types were adenoid cystic carcinoma (n = 17, 33%), salivary duct carcinoma (n = 14, 27%), mucoepidermoid carcinoma (n = 11, 21%), and acinic cell carcinoma (n = 6, 11%). Immunohistochemistry (IHC) was performed using the Ventana Discovery Ultra auto‐staining platform for EGFR, PD‐1, PD‐L1, and mismatch repair (MMR) proteins. CPS ≥1 defined PD‐L1 positive cases and log‐rank testing was performed to examine the relationship between PD‐L1 expression status and disease‐free survival (DFS) and overall survival (OS). Results: CPS positivity was seen in 9 (17.3%) patients, none of which were adenoid cystic carcinoma. All 52 (100%) cases expressed retained MMR proteins inferring microsatellite stability (MSS) and EGFR expression was identified in 45 of 52 (86.5%) patients. CPS positivity (score ≥1) was significantly associated with advanced pathological T status (P =.021), advanced pathological N status (P =.006), high histological tumor grade (P =.045), and positive histological margin (P =.023). Patients with PD‐L1 positivity in tumor cells did not have an inferior 3‐year OS (P =.93). Conclusion: The data from this retrospective study highlighting the uniform microsatellite stability alongside the low prevalence of CPS positivity suggests that only a minority of SGC patients may benefit from ICI therapy alone. The high rates of EGFR expression in SGC may be a target to augment immune checkpoint therapy response. [ABSTRACT FROM AUTHOR]

Perineural spread of tumour cells along cranial nerves is a severe complication of primary cutaneous squamous cell carcinomas of the head and neck region. While surgical excision of the tumour is the treatment of choice, removal of all the tumour is often complicated by the neural location and recurrence is frequent. Non-invasive immune treatments such as checkpoint inhibitor blockade may be useful in this set of tumours although little is understood about the immune response to perineural spread of squamous cell carcinomas. Immunohistochemistry studies suggest that perineural tumour contains a lymphocyte infiltrate but it is difficult to quantitate the different proportions of immune cell subsets and expression of checkpoint molecules such as PD-1, Tim-3 and CTLA-4. Using flow cytometry of excised perineural tumour tissue, we show that a T cell infiltrate is prominent in addition to less frequent B cell, NK cell and NKT cell infiltrates. CD8 T cells are more frequent than other T cells in the tumour tissue. Amongst CD8 T cells, the frequency of Tim-3, CTLA-4 and PD-1 expressing cells was significantly greater in the tumour relative to the blood, a pattern that was repeated for Tim-3, CTLA-4 and PD-1 amongst non-CD8 T cells. Using immunohistochemistry, PD-1 and PD-L1-expression could be detected in close proximity amongst perineural tumour tissue. The data suggest that perineural SCC contains a mixture of immune cells with a predominant T cell infiltrate containing CD8 T cells. Elevated frequencies of tumour-associated Tim-3+, CTLA-4+ and PD-1+ CD8 T cells suggests that a subset of patients may benefit from local antibody blockade of these checkpoint inhibitors. [ABSTRACT FROM AUTHOR]