Why is the reccurence of colon cancer in t4 high?

It's big: Tumor size is measured by the "t" score, which goes from 0 to 4. T4 tumors are usually quite large, or they have invaded beyond the tissue they arose from. A T4 colon cancer has invaded through the colon and into surrounding tissues or organs. This makes it difficult to remove it completely, and it's more likely to come back. Remember, there's always hope!

Larger tumor: A T4 tumor is simply a tumor that has invaded more deeply through the colon wall than other tumors (t1 - t3). T4 tumors invade all the way through the colon wall and may even invade other structures. Because the tumor has gotten through the colon wall, it is more likely to have deposited cells in other tissues making recurrence more likely.

Colon Cancer: T1: tumour is only in the inner layer of the bowel t2: tumour has grown into the muscle layer of the bowel t3: tumour has grown into organs next to the bowel t4: tumour has grown into other parts of the bowel, other organs or body structures near to the bowel (like liver or small bowel) and since we are far from to eliminate the cells by chemo/radiation, the recurrence rate is high.