PENK and cancer: Among the 59 genes in the MSC gene set, the expression levels of IGFBP3, TAGLN, COL6A1, COL6A2, LUM, COL1A2, COL3A1, and COL1A1 were significantly higher, whereas those of PITX2, HAS1, TRHDE, and PENK were significantly lower than those of other MSC-related genes in the 33 cancer types (Fig. 1c and d).