[U.S. Food and Drug Administration]

FDA Medical Bulletin * October 1996 * Volume 26 Number 3

RADIOLABELED ANTIBODIES
FOR DIAGNOSTIC IMAGING

Over the past year, the FDA advisory committees recommended market approval of four radiolabeled antibodies for diagnostic imaging. At this time, the Agency has granted a license to three of the manufacturers to market their imaging agents.

CEA-Scan is a murine monoclonal antibody fragment linked to technetium 99m. CEA-Scan is reactive with carcinoembryonic antigen, a tumor marker for cancer of the colon and rectum. It is indicated with other standard diagnostic modalities for the detection of recurrent and/or metastatic colorectal cancer. In conjunction with computed tomography, the agent provides additional information about the presence, location, and extent of disease. CEA-Scan was approved June 26, 1996.

Myoscint is a murine monoclonal antibody Fab fragment linked to indium-111. Indium-111 Myoscint binds with high affinity and specificity to human cardiac myosin, which is exposed following a loss of integrity of the myocyte cell membrane. It is a cardiac imaging agent indicated for detecting the presence and location of myocardial injury in patients with suspected myocardial infarction. Use of Myoscint is anticipated in situations where electrocardiography and cardiac enzymes are nondiagnostic. Myoscint was approved July 3, 1996.

Verluma is a monoclonal antibody Fab fragment linked to technetium-99m. Verluma identifies advanced stage disease in patients with small cell lung cancer (SCLC). The determination of disease stage has important prognostic and therapeutic implications. In the clinical trial involving 89 patients with confirmed SCLC, technetium-labeled Verluma accurately determined whether the disease was extensive or limited 82 percent of the time. If the test indicated extensive disease, the result was true in 94 percent of the patients. However, if the test indicated limited disease, it was less valuable as a diagnostic aid, failing to image tumors in some body organs in approximately 23 percent of patients. Because of these false negative readings, additional standard diagnostic tests, such as bone or computerized tomography scan (CT scan), or a bone marrow biopsy should be performed when limited disease is found. Verluma was approved August 20, 1996.

ProstaScint is a monoclonal antibody imaging agent linked to indium-111. It seeks out and attaches to prostate cancer and its metastases. ProstaScint images can aid in patient management by helping identify when the cancer has spread outside the prostatic bed to regional lymph nodes or to distant soft tissue sites. Surgical resection of the prostate is not indicated for patients whose disease has spread outside the prostatic bed.

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