Factors affecting uptake of radioactive agents by tumour and other tissues

The subject of factors that affect the uptake of radioactive agents by tumour and other tissues is a broad and complicated one. Factors that may have considerable bearing on the relative affinity of tumour tissue for such agents are, in general, the following: (1) vascularity, blood flow, and interstitial fluid space; (2) uptake of a protein-bound form of the agent; (3) cell proliferation; (4) presence of carrier; (5) capillary and cell permeability; (6) presence of inflammation; and (7) pH. Certain tumour-localizing processes are based on the specific properties of the tissues in question, i.e. radioiodine for functioning thyroid carcinoma, bone seekers for bone lesions, etc., but there is as yet still no clear indication of the basic process(es) involved in the tumour-localization of agents such as 67Ga and others on which to base projections as to new materials that might be more specific for tumour tissue in general. (author)