It is more serious than a stage 1 cancer... There are things that can be done if it can easily be removed. My father had colon cancer and they removed 18 inches of the colon and he lived another 45 years.
At stage 3 it cannot be easily removed.
How serious it is depends on which stage 3 they have the 5 year survival rate ranges from 79% to 50%.
At this stage it is not easy to cure. Easy to cure is when it is cured on colonoscopy.