In a normal cell signal, a growth factor binds to a receptor in the cell membrane, the signal gets relayed molecule to molecule until it gets its message to the transcription factor which regulates gene activity and so regulates the genes controlling cell division. What happens in cancer cells

In cancerous cell,  telomerase expresses and enhances the cell cycle division

Explanation:

In Cancer,  cells divides uncontrollably as once the cell cycle is complete, the inhibitors do not restrict the cells from dividing further.  These positive regulators of cell cycle if not controlled leads to continuous break down of cell and hence the cancer.  

In a cancerous cell, enzyme reversing the wearing down of chromosome at the end of all cell cycle i.e telomerase expresses which in normal cases stops the cell division.