My Husband Was Recently Told He Has A High Level

My husband was recently told he has a high level of abnormal cells in the Sigmoid area of the colon. They're calling this dysplasia, abnormal cells. They will be performing a colon colectomy , cutting away the part of the colon that has these abnormal cells, His doctor feels about one quarter of the colon shall have to be removed. Could these abnormal cells inside the colon wall be cancerous? How could that affect the amount of colon taken? Will they keep taking as much of the colon as they need to to get all the cells that are cancerous, if that is what they find. His doctor has told him of the necessity for doing this quickly because of the high level of abnormal cells or dysplasia. Can these abnormal cells often be cancerous when they go into the colon wall and how does that change the surgery.