GDF15 and esophageal squamous cell carcinoma: Several studies have shown that GDF15 can induce PI3K/Akt and Erk1/2 activation in esophageal squamous cell carcinomas, breast, cervical, gastric and prostate cancers (56–59), while regarding brain tumors it was found that an overexpression of GDF15 in brain cancer cells did not affected Erk1/2 activation (60).