Cancer diagnosis. The role of tumor-imaging radiopharmaceuticals.

Several radiopharmaceuticals have recently been shown to have a considerable affinity for malignant tissue. All the tumor-seeking radiopharmaceuticals in current use are nonspecific and may also be picked up by benign tumors and infectious processes, including abscess and granuloma. The sensitivity of the tumor-imaging procedure depends on the radiopharmaceutical employed, the type of tumor, its size and location, and previous or current treatment. Gallium-67 citrate (67Ga), the most widely used tumor-seeking radiopharmaceutical, seems to have its greatest value in detecting bronchogenic carcinomas irrespective of cell type. The sensitivity for lung cancer in 489 studies was 93 per cent. Gallium-67 is also of great value in the staging of Hodgkin's disease, in which its sensitivity is 87 per cent. Non-Hdgkin's lymphomas are detected with only slightly lower sensitivity. There is, in fact, evidence that 67Ga is at least complemenatry, if not more sensitive than lymphangiography, in the staging of lymphoma. However, adenocarcinomas originating in the gastrointestinal tract are detected by 67Ga with a sensitivity of only about 40 per cent, whereas various chelates of bleomycin (including 111In-Bleo, 99mTc-Bleo and 57Co-Bleo) detect adenocarcinoma of the gastrointestinal tract with considerably higher sensitivity. In the few studies available comparing bleomycin chelates, 57Co-Bleo and 99mTc-Bleo appear to be more sensitive in detecting tumor than 111In-Bleo. Other tumor-seeking radiopharmaceuticasl which have been employed with somewhat less success include selenium compounds, labeled pyrimidines, several inorganic cations, lanthanide chelates and labeled proteins. Yet to be evaulated clinically is the efficacy of radiolabeled antibodies which are specific for tumor antigens, such as 131I-anti-CEA (carcinoembryonic antigen).