Technetium 99m-labeled IMMU-4, a monoclonal antibody against carcinoembryonic antigen, for imaging of occult recurrent colorectal cancer in patients with rising serum carcinoembryonic antigen levels.

Abstract

We tested whether nuclear imaging with technetium 99m-labeled murine monoclonal antibody (MoAb) against carcinoembryonic antigen (CEA) IMMU-4 will detect recurrent colorectal disease in patients with a rising serum CEA level but negative abdominal and pelvic computed tomographic (CT) scan, chest radiograph, and colonoscopy, or barium enema. Sixteen patients with completely resected, CEA-producing colorectal cancer were given 1 mg of 99mTc-labeled IMMU-4 intravenously with no toxic side effects. Planar and single-photon emission CT (SPECT) scans were acquired at 6 hours. Fifteen patients underwent an exploratory laparotomy at 24 hours. Results of the scintigraphy were correlated with surgical findings. Twelve of 15 patients (80%) had true-positive (TP) scans when correlated with surgery. Two of 15 (13%) had true-negative (TN) scans inasmuch as exploratory laparotomy failed to detect recurrent disease. A false-positive (FP) scan was obtained in one of 15 (7%). There were no false-negative (FN) scans. Sensitivity, specificity, accuracy, and the positive predictive value (PPV) were 100%, 67%, 93%, and 92%, respectively. Twenty-six histologically confirmed areas of malignancy were found and correlated with areas of increased activity seen on IMMU-4 scintigraphy. Twenty-one were TP; five were not detected by scintigraphy and were thus considered to be FN. There were five FP lesions and 25 TN regions. Sensitivity, specificity, accuracy, and the PPV in these 26 cancer tissues were 81%, 83%, 82%, and 81%, respectively. The median radioactivity ratio of tumorous tissue to normal tissue was 3.33, with a range of 0.89 to 17.16. These results suggest that 99mTc IMMU-4 scintigraphy is an important addition to the armamentarium available for diagnostic imaging and may help detect occult metastatic cancer missed by abdominal and pelvic CT in patients with rising CEA levels.