Stage 1:
Cells are programmed to grow, perform a job, and die. A cell becomes cancerous when it ignores its DNA programming rules. It grows, becomes abnormal, and  invades nearby areas.

Stage 2:
These abnormal cells replicate over and over and become a tumour. The tumour crowds  out (bullies and kills) normal cells.

Stage 3:
The tumour continues to grow and expand. It reaches your blood vessels and lymph nodes (kind of a superhighway to other organs)!

Stage 4:
The cancer spreads to, and invades, other parts of your body. This primary cancer has now become a secondary cancer.