How cells become cancerous is a process researchers are still trying to fully understand. Generally, normal cells grow and multiply through controlled cell division, where old and damaged sells are replaced after they die by new cells. Sometimes this process stops working, leading cells to start growing uncontrollably and develop into a tumor.

Traditionally, cancer treatments like chemotherapy, immunotherapy, radiation and surgery focus on killing cancer cells. 

Accumulating evidence is showing that cancer stem cells can differentiate into multiple cell types, including noncancerous cells. Researchers are taking advantage of this fact through a type of treatment called differentiation therapy.

https://theconversation.com/amp/triggering-cancer-cells-to-become-normal-cells-how-stem-cell-therapies-can-provide-new-ways-to-stop-tumors-from-spreading-or-growing-back-191559