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AimsCollecting duct carcinoma (CDC) and fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) have similar histological morphologies and both show a poor prognosis. Programmed death ligand 1 (PD-L1) inhibitor has been approved for the treatment of RCC. However, tumour-infiltrating neutrophils stimulated by interleukin-8 (IL-8) interfere with PD-L1 inhibitors. Here, we retrospectively analysed PD-L1 and IL-8 expression, and examined its relationship with infiltrating immune cells.MethodsNine cases of CDC and seven cases of FH-deficient RCC were selected. We defined PD-L1 and IL-8 expression by the Tumour Proportion Score and Combined Positive Score (CPS). We counted the numbers of CD8+, CXCR2+, CD11b+, CD66b+and CD33+immune cells located in the tumour components.ResultsA number of CXCR2+(p=0.0058), CD11b+(p=0.0070) and CD66b+(p=0.0067) immune cells infiltrating into CDC were significantly higher than those infiltrating into FH-deficient RCC. In CDC, PD-L1 expression was correlated with a high density of CD8+lymphocytes (p=0.0389), but was not in FH-deficient RCC (p=0.6985). IL-8 CPS was significantly higher in CDC than in FH-deficient RCC (p=0.0069). In addition, among the CDC cases, IL-8 CPS showed significant positive correlations with CXCR2+, CD11b+and CD66b+immune cell densities (p=0.0250, p=0.0104 and p=0.0374, respectively), whereas FH-deficient RCC showed no significant correlations between IL-8 CPS and immune cell densities.ConclusionsOur results suggest the difference of each tumour microenvironment between CDC and FH-deficient RCC, and IL-8 is a potential therapeutic target for treating CDC, but not FH-deficient RCC.