Of the four FFARs, FFAR2 expression was significantly decreased in lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) (Fig. 1A, left, LUAD; right, LUSC: *P < 0.05), whereas no significant changes were observed in the other three FFARs, including FFAR1, FFAR3, and FFAR4 (Supplementary Figure S1A, FFAR1; Figure S1B, FFAR3; Figure S1C, FFAR4). Here, FFAR4 is linked to lung adenocarcinoma.