MAPK8 and breast cancer: Furthermore, analysis of cancer cells with active c‐Jun in metastatic nodules of lungs from mice injected with MDA231‐LM2 breast cancer cells revealed that over 50% of cancer cells in micrometastases (day 7 post‐injection) exhibited active JNK signaling whereas less than 15% were observed in macrometastases (day 21 post‐injection), often associated with the invasive front (Fig 1E and F).