KRT18 and small cell lung carcinoma: Among the proteins confirmed on tissue transcriptome level, six are also detectable in human blood plasma by MS, namely tyrosine–protein kinase receptor UFO (AXL, upregulated in SCLC‐Y), basal cell adhesion molecule (BCAM, upregulated in SCLC‐A vs. ‐N), GTP‐binding protein 1 (GTPBP1, upregulated in SCLC‐N vs. ‐A), keratin‐18 (KRT18, upregulated in SCLC‐A vs. ‐N), noelin (OLFM1, upregulated in SCLC‐N vs. ‐A) and phospholipase C‐gamma‐2 (PLCG2, upregulated in SCLC‐P).