CCNE1 and neoplasm: Five isoforms of cyclin E, ranging in size from 33 to 44 kDa, have been identified in tumors over-expressing cyclin E. These low molecular weight forms of cyclin E (LMW-E) are generated through post-translational cleavage of full-length cyclin E by the elastase family of serine proteases in tumor cells [6], [7].