GDF15 and malignant colon neoplasm: In 2001, the Eling group identified what they called nonsteroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1) using subtractive cloning in NSAID-treated colon cancer cells and used sequence analysis to determine that MIC-1, placental transforming growth factor-β (PTGF-β), prostate-derived factor (PDF), placental bone morphogenic protein (PLAB), and NAG-1 all encoded the same gene (7).