The large intestine is made of different segments: the ascending colon, transverse colon, descending colon, sigmoid colon and rectum ending in the anal canal. Its role is predominantly to convert liquid stools into solid faeces in addition to functions. Cancers arising in the large intestines are called colorectal cancers. The rectal cancers are considered separately because of their unique behavior, response to different cancer treatments and the peculiar anatomical location of the rectum.
Usually, the colorectal cancers start as a small polyp which over years can transform into invasive cancer. This polyp to cancer transformation gives us an insight into cancer development and allows us to intervene at different points to prevent or treat cancer. Screening colonoscopies can detect the precancerous polyps and removal of the endoscopically effective prevents cancer thus making it a truly preventable cancer.
Right-sided Colon cancer in early stages may not have any symptoms or present non-specifically as anaemia or increased frequency of stools or abdominal discomfort. Early left-sided colon cancers and rectal cancers can present as the alteration in bowel habits, blood in stools or mucus in stools. Late cancers can present as bowel obstruction. Rarely the first presentation can be that of a distant spread like bone pain, lung, or liver spread. Patients can also be detected to have colorectal cancer during routine screening.
Dr Guruprasad Bhat 