Case of the Month—September 2003

Colorectal Cancer—Recurrence of Disease

History
A 45-year-old male with a history of rectal cancer was originally diagnosed in August 2000. On initial diagnosis, the patient was found to have a 12.5-cm mass located in the rectum. Low anterior resection was performed. Three of the six lymph nodes removed were found to be positive for cancer. The patient underwent both radiation therapy and adjuvant chemotherapy.

In November 2002, the patient presented with rising CEA but normal liver enzymes. A CT of the abdomen and pelvis in January 2003 showed no evidence of metastatic disease. A PET scan was requested for further evaluation.

Findings
The PET study demonstrated a large focus of intense uptake in the liver, along with multiple foci in the para-caval and para-aortic regions.

Follow Up
Follow-up CT after the PET FDG (fluorodeoxyglucose) scan confirmed the presence of metastatic disease.


Para-aortic lymph node	Para-caval lymph nodes	Liver uptake

How Did PET Help?
PET was able to detect metastatic disease that had not been identified by conventional CT imaging.

Discussion
PET has been approved by Medicare for diagnosis, staging, and restaging of colorectal cancer. Although PET is very sensitive for detecting colon cancer, it has low specificity due to normal excretion of radiotracer in the bowel. Thus its application for diagnosis ofprimary colon cancer is limited. PET has proven to be more accurate than CT and/or MRI in detecting local and distant metastasis.1 Clinically, PET is useful to differentiate scar from active tumor in post-op patients, to detect recurrent cancer, to assess operability for patients with liver metastasis, and to monitor therapy response.

1. S. S. Gambhir et al, Journal of Nuclear Medicine, 42 (5 Supplement), 2001, 9S-12S.

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