Here, we use isogenic Beas-2B bronchial epithelial cell lines expressing EML4-ALK V1 or V3, as well as ALK-positive NSCLC patient cells that express V1 (H3122 cells) or V3 (H2228 cells), to show that EML4-ALK V3 but not V1 leads to hyperstabilized K-fibers in mitosis, as well as errors in chromosome congression and segregation. The gene discussed is EML4; the disease is non-small cell lung carcinoma.