Colorectal cancer, like other types, can be diagnosed in several different stages, depending on the extent that the disease has progressed. There are five stages to colon and rectal cancers, 0 to IV. A patient’s prognosis gets progressively worse with each advancing stage, with IV being the most serious stage of colorectal cancer.

A stage 0 diagnosis offers the best prognosis, because the cancer is in its earliest stages and is most easily treatable. Also known as carcinoma in situ, this stage is reached when the upper layer of tissue in the colon called the mucosa shows the presence of abnormal cells. Stage I colorectal cancer can be diagnosed when the cancer spreads through the mucosa and into the submucosa or into the bowel muscle but not through it.

Stage II colorectal cancer can be diagnosed when the cancer has grown through the colon or rectal muscle and has also invaded nearby organs, such as bowel loops, ovaries, bladder or uterus. A stage III diagnosis means the cancer has breached local lymph nodes in addition to local organs. The worst diagnosis, stage IV, means the cancer has spread to lymph nodes or organs in distant parts of the body.