Cancer typically has four stages according to its severity and the extent of spread.
Stage I is usually when the disease is confined to the site/organ it has affected
Stage 2 when it has started involving locally or gone to closest or the first lymph nodes
Stage 3 when it has started to spread to more far away, surrounding organs, distant lymph nodes
Stage 4 when very far sites are involved or multiple sites in the complete body are involved . It usually occurs when the cancer has spread through blood vessels to the whole body.
Note : every type of cancer has different staging according to the international guidelines, this is just an overview of the staging.