DETECTION OF CARTILAGINOUS TUMORS WITH SELENIUM 75.

Abstract

Tumor detection by means of radioactive elements or labeled compounds selectively fixed on neoplastic tissue is doubtless the most elegant and precise method of oncological diagnosis possible. To date, however, tumors for which an effective tracer has been found are scarce, and therefore the investigation of new elements with a specific affinity to some type of neoplasm is of great interest. Experimental studies have demonstrated that radioactive sulfur, administered in the form of sulfate, fixes to a great extent in cartilage, with little retention in remaining tissue. In a first phase, the radiosulfuris trapped by chondrocytes. These rapidly incorporate it into the molecule ofchondroitin sulfate, where it becomes stable and then passes to the cartilaginous matrix. Here it remains for a long time. It is known that some differentiated tumors have metabolic patterns similar to those of the tissue of origin. This is true of cartilaginous tumors, in which the metachromatic staining properties indicate specifically the presence of sulfuric esters of polysaccharides. It appeared likely, therefore, that radioactive sulfur given to man would be taken up selectively by neoplastic as well as by normal cartilage. Layton (1) in in vitro tissue culture and Gottschalk and Allen (2, 3) studied operative specimens removed after the injection of S35. They demonstrated that in cartilaginous tumors the fixation of radioactive sulfur is increased in comparison with that in other tissues and normal cartilage. The most extensive fixation occurred in the areas of the most active growth. Efforts have been made to take advantage of this property in the treatment of chondrosarcomas by administering high doses of S35 (1 curie). The results, however, have been of scant encouragement, probably on account of the radioresistance of this type of tumor (4–6). Of all the sulfur radioactive isotopes, S35 is the only one which is utilizable in practice. S37 has a half-life of five minutes, and S38 is very difficult to obtain. S35 is a pure beta emitter with a radiation of low penetration (maximum beta energy, 0.167 Mev). Consequently, while it is excellent for autoradiographic studies, it cannot be employed for the diagnosis of tumor detection by external counting. Its excellent fixation on the cartilaginous tumors, however, makes its utilization feasible, at least in theory. Because of this we thought of the possibility of changing the sulfur for an element of similar chemical characteristics but possessing a gamma emitter. To us, selenium appeared the most adequate substitute, and out of its different radioactive isotopes we selected Se75 as the most convenient and one with highly suitable physical characteristics. Se75 is produced in a reactor from the Se74 by reaction (n,γ).