To be or not to be a proliferation marker?

Whether it is nobler in the mind to suffer the slings and arrows of outrageous proliferation, or to take arms against stroma, and favor metastasis… This pastiche of Hamlet's famous monologue illustrates recent reports on the paradoxical functions of well-established proliferation markers such as c-Myc or cyclin A2 that have revealed their ambiguous roles in the control of proliferation and metastasis. On the one hand, overexpression of c-Myc, while stimulating local proliferation, inhibits invasiveness of cancer cells, whereas on the other, downregulation of cyclin A2 leads to increased motility of transformed cells.