Final answer:
The tumor marker CEA is used in monitoring colorectal cancer, and nodal involvement is the most important prognostic factor. Elevated CEA levels can indicate cancer recurrence, making it a valuable tool for tracking post-operative patients. Alongside other screening methods like colonoscopy, CEA is instrumental in the diagnosis and management of colorectal cancer.
Step-by-step explanation:
The monitoring of the tumor marker CEA (carcinoembryonic antigen) is useful in colorectal cancer. Nodal involvement is the most important prognostic variable in assessing the extent and prognosis of the disease. Tumor markers are substances that can be found in the blood, urine, or body tissues and may be elevated in the presence of cancer. They are not always specific to one type of cancer, but their levels can be monitored to track the progression of the disease or the response to treatment. In colorectal cancer, CEA is a tumor marker that can indicate the return of cancer before it is identifiable through imaging or physical examination.
Overall, tumor markers like CEA, along with screening methods such as fecal occult blood tests and colonoscopy, play a crucial role in the diagnosis, monitoring, and potential prevention of colorectal cancer by identifying and removing precancerous polyps.