Final answer:
A rising CEA level in a patient with previous colon cancer may indicate cancer recurrence. Diagnostic tests such as PET scans should be performed to evaluate the presence of recurrent bowel cancer.
Step-by-step explanation:
A rising CEA level in a patient with a history of treated bowel cancer can be an early sign of cancer recurrence. This can occur before the cancer site can be identified through imaging or examination. Therefore, when a patient's CEA level spikes after 2 years, the next step in evaluation would be to perform diagnostic tests such as PET scans to determine the presence of a recurrent bowel cancer.