The Lentiviral delivery method of shRNA has been used to knockdown JNK isoforms in different cell lines including human epithelial,18 human liver cancer,19 and mouse mammary tumor cells.20 As this has allowed differences in isoform function to be determined in these studies, we used lentiviral shRNA to generate MCF‐7 cell lines containing stable knockdown of JNK1, JNK2, and JNK1/2. The gene discussed is MAPK8; the disease is breast cancer.