CTSG and breast cancer: To address experimentally whether JNK signaling contributes to breast cancer metastasis to lungs, MDA231‐LM2 or SUM159‐LM1 cells were injected bilaterally into the fourth mammary fat pads of NOD.Cg‐PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice.