Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
>CEA-Scan (Australian Radioisotopes)
vials containing 1.25 mg lyophilised arcitumomab for reconstitution with sodium-pertechnetatein saline
Approved indication: imaging of advanced colorectal cancer
>Carcinoembryonic antigen (CEA) is found in the serum of patients with colorectal cancers. It can be used in monitoring these patients for local recurrences or metastases. Attaching a radioactive label to an antibody (arcitumomab) to CEA helps to localise where the tumour cells producing the CEA are.
>Arcitumomab is made by exposing mouse spleen cells to human CEA. These cells produce an antibody from which the arcitumomab fragment is extracted. Arcitumomab is mixed with a technetium-containing radionuclide and diluted before being injected intravenously. The technetium disintegrates giving off gamma rays. It has a half-life of six hours and 28% of the radiolabel is excreted in the urine within 24 hours. Imaging should take place 2-5 hours after the injection.
>In one trial, 40 patients with resected rectal cancer were followed up for five years with CEA immunoscintigraphy in addition to routine surveillance. Sixteen patients developed recurrent cancer. Although only six of these patients had increased serum CEA, immunoscintigraphy identified 82% of the tumours. The sensitivity for finding lesions was 94% and the specificity was 97%. This resulted in six patients having further surgery which could improve their survival. These patients had a mean survival of 35 months compared to 21 months in a group of historic controls.1
>The adverse reactions to the injection have included itching, urticaria and other rashes. Some patients will develop antibodies to mouse protein.
>Although CEA immunoscintigraphy can help to identify local recurrences, it may not give surgeons all the information they need. In a comparison with positrone mission tomography (PET), CEA immunoscintigraphy did not detect all metastases in bone, lung and lymph nodes.2 Another small study found that PET is better at predicting which patients have respectable recurrent disease. In 16 patients having resections, PET had predicted respectable tumours in 81% while CEA immunoscintigraphy identified only 13% as resectable. CEA immunoscintigraphy was unable to show which patients had unresectable disease whereas PET predictions were correct in 90% of patients with unresectable disease.3
