What changes might cancer cells undergo that would stimulate them to reenter the cell cycle and continuously divide?

The presence of cyclins and cyclin-dependent kinases are the main regulators of cell cycle. Therefore, the excess of cyclin, due to a mutation in the genes for these proteins, that pushes the cycle forward cause the proliferation of cells. Also, a mutation in the tumor suppressor gene would cause a repression of tumor suppressor proteins which are significant in inhibiting progression of the cell cycle.

1.989×10^30 kg is the weight of the sun.