While GPRC5A was downregulated in both human lung adenocarcinoma (Figure 1B, left) and squamous cell lung carcinoma (Figure 1B, right), several candidate genes were also found to be upregulated in lung cancer tissues compared to normal ones, including keratin 18 (Krt18), lipocalin 2 (LCN2), ceruloplasmin (Cp), major histocompatibility complex class I-related (Mr1), desmoglein 2 (Dsg2), ectonucleotide pyrophophatase/phosphodiesterase 1 (Enpp1), and periostin (Postn) (Figure 1C–1E). Here, KRT18 is linked to lung adenocarcinoma.