Radiolabeled Peptide Offers New Diagnostic Tool for Colorectal Cancer

TORONTO--Visualization of gastrointestinal carcinomas is enhanced with the use of a radiolabeled peptide developed at the University of Vienna, according to a study presented at the 45th Annual Meeting of the Society of Nuclear Medicine (SNM).

Studies have shown that many GI tumors have receptors for vasoactive intestinal peptide (VIP), said Shuren Li, MD, Department of Nuclear Medicine, University of Vienna, and receptor scanning with iodine-123-labeled VIP (¹²³I-VIP) can identify hot spots associated with colorectal cancer.

"There is no cure for advanced colorectal cancer," Dr. Li said, "so early detection of disease influences the prognosis of the patients. We offer receptor scintigraphy as a way to identify small metastatic lesions and to differentiate lesions from operative scarring."

Eighty patients with confirmed colo-rectal adenocarcinoma underwent receptor scintigraphy with ¹²³I-VIP (1µg to 150 MBq). Two independent physicians evaluated each scan, and patients were followed for at least 6 months or until death with regular CT scans every 8 weeks. However, Dr. Li pointed out, all comparisons between ¹²³I-VIP and CT were done with scans taken within 4 weeks of each other.

Of the 80 patients, 13 were free of tumor after previous resection; 8 presented with primary tumors; 14 had locally recurrent tumors but no metastases; 10 had locally recurrent tumors with metastases to the liver, lung, or lymph nodes; and 35 had disease confined to organ metastases.

Fourteen of the patients with advanced colorectal cancer also presented with adenomatous polyps at the time of screening.

The ¹²³I-VIP scans were negative in all 13 curatively resected patients, Dr. Li reported. VIP receptor scans identified 7 (87%) of the 8 primary tumors and 21 (82%) of the 24 locally recurrent tumors. All 4 patients with lymph node metastases had positive scans; 25 (89%) of the 28 liver metastases were identified (Figure), as were 2 (67%) of the 3 lung metastases.

In four patients with relapsing cancer, the ¹²³I-VIP scans indicated the presence of disease before CT imaging. Also, in two patients with suspicious CT scans, the ¹²³I-VIP scan identified the areas as surgical scar tissue. There was no ¹²³I-VIP tracer uptake seen in the adeno-matous polyps.

Speaking at a press conference held in conjunction with the SNM meeting, Markus Raderer, MD, lead author of the study, said that "incorporation of VIP into the clinical workup of patients with a history of colorectal cancer can provide additional information to conventional radiologic methods, both in the staging of patients with documented disease and in patients with suspected recurrence."

Dr. Raderer noted that the researchers are currently developing a technetium-99m-labeled VIP, "which would clearly facilitate widespread use of this compound." His group is also conducting a study comparing ¹²³I-VIP with fluorine-18 fluorodeoxyglucose (FDG) imaging with PET in patients with colorectal cancer.