In This Section

Colorectal Cancer

Colorectal cancer occurs when certain cells within the large intestine grow in an uncontrolled, abnormal, manner. Cancer that begins in the last 6-8 inches of the colon is called rectal cancer. Together, they are often referred to as colorectal cancer.

According to estimates from the American Cancer Society, more than 141,000 new cases of colon and rectum cancer will be diagnosed in the United States and more than 50,000 people will die from the disease in 2011. Colorectal cancer is the fourth leading cause of cancer deaths among both men and women.

New developments in molecular imaging technologies are dramatically improving the ways in which colorectal cancer is diagnosed and treated. Research in molecular imaging is also contributing to our understanding of the disease and directing more effective care of patients with colorectal cancer.

Positron emission tomography (PET) scanning and PET combined with computed tomography (PET-CT) is used for colorectal cancer.

What is PET?

PET involves the use of an imaging device (PET scanner) and a tiny amount of radiotracer that is injected into the patient’s bloodstream. A frequently used PET radiotracer is 18F-fluorodeoxyglucose (FDG), which the body treats like the simple sugar glucose. It usually takes between 30 and 60 minutes for the FDG distribution throughout the body to become fixed. A CT is also obtained on the same machine so the FDG and CT scans can be fused together and compared.

How is PET used for colorectal cancers?

  • Diagnose and stage: by determining the location of the cancer and where the cancer has spread in the body.
  • Plan treatment: by determining a site that is appropriate for biopsy and in research studies helping select the best therapy based on the unique biology of the cancer and of the patient.
  • Evaluate how the cancer responds to treatment.
  • Manage ongoing care: by early detection of the cancer coming back.


Advantages of PET

  • PET is better than CT for staging colorectal cancer and is especially valuable for detecting cancer recurrences
  • PET is able to tell apart and post-treatment scarring in the colon and the cancer coming back
  • PET is able to see if the cancer is has spread to the liver or lung, providing valuable information to the doctor in planning treatment
  • PET is useful in detecting where the cancer has come back in patients who have an increased blood protein called carcinoembryonic antigen (CEA).


A 64-y-old female patient with colorectal cancer restaged for tumor recurrence 6 mo after chemotherapy.

A 64 year-old female patient with colorectal cancer restaged for tumor reccurrence 6 months after chemotherapy.  Tumor markers and CT scan were negative for tumor recurrence. FDG PET images show large focus of increased tracer uptake suggesting mesenteric lymph node involvement (arrows). Management was changed from no therapy to chemotherapy.


Download the fact sheet: Molecular Imaging and Colorectal Cancer