GDF15 and colorectal carcinoma: In light of our observation that senescent fibroblasts promote cell proliferation, migration, and invasion in colorectal adenoma and CRC cell lines, and the discovery of GDF15 among the most up‐regulated genes in the senescent fibroblasts, we next assessed whether secreted GDF15 from senescent fibroblasts is a mediator of the pro‐tumorigenic effects of the senescent cells on colon epithelial cells.