Cluster C1 was primarily represented by MKN-45 cells isolated from tumor xenografts (25–30% of total xenograft MKN-45 cells and less than 5% from pre-xenograft cells), and its defining gene set included keratin family genes (KRT19, KRT8), CXCL1, CD9 (tetraspanin-29), IFI27, and IL-1 receptor (IL1R2), which are associated with inflammation (Figure 2E and Supplemental Figure S1) [41]. Here, CD9 is linked to neoplasm.