Tumour imaging radiopharmaceuticals.

32P, 131I-labeleed human serum albumin, 75Se-seleno-methionine, 107Hg-chlormerodrin, 67Ga-citrate and labelled bleomycin compounds, among others are discussed with particular respect to their observed clinical characteristics and suggested mechanisms of uptake. It is shown that there are striking similarities in the kinds of tumours demonstrable by these agents and that all of them may be taken up into inflammatory exudates. It is suggested that, while differences in the metabolism of each agent clearly exist, their mechanism of tumour uptake may be predominantly non-specific. It is concluded that radionuclide tumour imaging is of potential value mainly from the point of view of ease of whole body scanning for follow-up purposes and whereas other diagnostic methods may be more accurate in specific areas, ease of whole body screening is rarely a feature of these techniques. Methods for studying human cancer are necessarily restricted and the tumour imaging technique provides a unique, dynamic means of tumour observation. From the clinical point of view, the questions of why some tumours image well and others do not, what is the effect of treatment on uptake and how specific is the technique, are of most importance. In order to improve tumour imanging, more emphasis must be given to improving the lesion: background radioactivity ratio of the agents rather than attempting to improve detection equipment.