Arginase-1 and the adenosine pathway, which were major regulators of antitumor immunity, might have had a role in modifying the impact of immunotherapy. Researchers looked at how the immune-related indicators were expressed in thymic epithelial tumors (TETs) and small cell lung cancer (SCLC), 2 solid malignancies where immune checkpoint inhibitors were used. Tissue microarrays of 123 TET (110 thymomas and 13 thymic carcinomas) and 125 SCLC patients were used to performing immunohistochemical labeling. Arginase-1, CD39, CD73, A2AR, PD-L2, and CD15 were evaluated for their expression profiles in immune-related indicators. Clinical data were also used to link the expression profile. Arginase-1 was not detected in any of the samples. Positive staining for CD39, CD73, and A2AR in the adenosine pathway was 4.9%, 2.5%, and 69.2% in TETs and 0%, 1.7%, and 50.8% in SCLC. In TETs, CD39 expression was linked to lower disease-related survival (hazard ratio [HR], 10.36; 95% confidence interval [CI], 2.01-53.47; P=.005) and a shorter time-to-progression (HR, 11.35; 95% confidence interval [CI], 2.11-61.23; P=.005). In TETs, other indicators were not linked to disease-related survival or progression time. In SCLC, no biomarker was linked to survival. TETs and SCLC had no detectable arginase-1. In both TETs and SCLC, markers of the adenosine pathway were expressed. CD39 expression in tumor cells might have helped doctors identify individuals with TETs who had a poor prognosis.