The expression of programed death ligand‐1 could be related with unfavorable prognosis in salivary duct carcinoma

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Salivary duct carcinoma (<jats:styled-content style="fixed-case">SDC</jats:styled-content>) is a rare tumor occurring in the salivary gland. <jats:styled-content style="fixed-case">SDC</jats:styled-content> is a highly aggressive tumor and its prognosis is extremely poor. Effective treatments in advanced <jats:styled-content style="fixed-case">SDC</jats:styled-content> have not yet been established. Recently, immune checkpoint inhibitors have paved the way for the treatment of various malignancies. We examined the expressions of programed death ligand (<jats:styled-content style="fixed-case">PD</jats:styled-content>‐L) 1/<jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 and programed death (<jats:styled-content style="fixed-case">PD</jats:styled-content>‐1), and the correlation of clinicopathological findings.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We examined 18 cases of <jats:styled-content style="fixed-case">SDC</jats:styled-content> and conducted immunohistochemical staining using formalin‐fixed paraffin‐embedded full‐face sections.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The expression of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 and <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 in tumor cells was observed in nine cases (50%) and 14 cases (78%), respectively. Cases with a high expression of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 and <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 were found in four (22%) and seven cases (39%), respectively. The cases with a high expression of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 showed significantly shorter overall survival compared to those with low <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 expression and null expression. We also examined the expression of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1/<jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 and <jats:styled-content style="fixed-case">PD</jats:styled-content>‐1 of tumor‐infiltrating mononuclear cells (<jats:styled-content style="fixed-case">TIMC</jats:styled-content>) in stroma. The expressions of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 in tumor cells and stroma had a significant correlation. Association between the expressions of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 in tumor cells and those of <jats:styled-content style="fixed-case">PD</jats:styled-content>‐1 in stroma was significant. However, <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 expression in the tumor had no significant correlation with expression in <jats:styled-content style="fixed-case">TIMC</jats:styled-content>s. <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1, <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L2 and <jats:styled-content style="fixed-case">PD</jats:styled-content>‐1 expressions in stroma were not associated with patient prognosis.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>High <jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 expression in <jats:styled-content style="fixed-case">SDC</jats:styled-content> was strongly associated with unfavorable prognosis, indicating that <jats:styled-content style="fixed-case">PD</jats:styled-content>‐1/<jats:styled-content style="fixed-case">PD</jats:styled-content>‐L1 inhibitors could be effective in <jats:styled-content style="fixed-case">SDC</jats:styled-content>.</jats:p></jats:sec>