Chromosomal segregation 1 like (CSE1L) (also called cellular apoptosis susceptibility (CAS) and exportin-2; according to its official gene symbol (HGNC 2431; Entrez Gene 1434), we used CSE1L to describe both the protein (NP001307) and the gene in this article) was identified as the gene that rendered human breast cancer MCF-7 cells resistant to immunotoxins and turned out to be homologous to yeast CSE1 gene, which is involved in the regulation of chromatins (8, 9, 10). The gene discussed is CSE1L; the disease is breast carcinoma.