How does rectal cancer differ from colon cancer?

The tissue is not the same type.

For cancer cells to live in various tissues, they require unique characteristics.

'Markers' are characteristics specific to cancer cells found in each kind of tissue; these characteristics can be used to locate or even target specific cancer cells.

To exemplify this idea, suppose that a particular mutation in a particular gene of a cancer cell causes the cell to become more 'at home' in the rectum as opposed to the colon; in this case, the mutation would indicate rectal cancer rather than colon cancer.

You should be able to find lists of markers that differentiate the two types of cancers by conducting a literature search.

Rectal cancer occurs in the last several inches of the colon, whereas colon cancer can develop in any part of the colon. Both cancers share similar risk factors and symptoms, but rectal cancer may present with symptoms such as tenesmus or blood in the stool. Treatment options may vary depending on the stage and location of the cancer, but both may involve surgery, chemotherapy, and radiation therapy.