GDF15 and breast cancer: In breast cancer, PG could activate apoptosis by different signaling pathways including reducing Wnt/β-catenin, c-Jun N-terminal kinases/p38/RAD51 (JNK/p38/RAD51), or glycogen synthase kinase 3 beta/NAG-1 (GSK-3β/NAG-1), and inducing endoplasmic reticulum (ER) stress [17,18,19,20].