The Use of Radioactive Phosphorus in the Diagnosis of Thyroid Cancer

Abstract

Approximately twenty years ago it was first demonstrated that radioactive phosphorus (P32) uptake is selectively increased in malignant tissue (6, 11). During the past two decades P32 has been used to study numerous experimental and human tumors. Since thyroid cancer is often difficult to diagnose clinically, occasionally presenting a problem even to the pathologist examining microscopic sections, attention has been turned toward the diagnostic use of P32 uptake, particularly in solitary nodular and multinodular goiters. Method The P32-uptake test has been performed on a total of 61 patients with solitary nodular and multinodular goiters. These patients, including 47 women and 14 men, seventeen to seventy-seven years of age, were from the out-patient and in-patient services of the University of Minnesota Hospitals. They were given an oral dose of 500 microcuries of P32 in the form of sodium phosphate and were tested for uptake twenty-four hours later. With an eye-probe Geiger-Müller tube (Anton Laboratories Model 222), multiple counts were recorded over the thyroid nodule and over surrounding areas. Adjacent thyroid and anterior neck tissue served as a control to the suspicious nodule. During this study background counts averaged 10 cpm and counts over normal tissue averaged 110 cpm. The ratio of P32 uptake over the suspected tissue as compared with the normal tissue was calculated. An increase of P32 uptake over the nodule of 20 per cent or more was considered a positive test. In most instances the P32-uptake test was performed prior to any I113-uptake studies. Since P32 is purely a beta-particle emitter, I131 studies can be carried out successfully immediately following its use. When I131 was administered first, it was necessary to delay the P32 test for at least three weeks, until residual iodine radioactivity had decreased to a minimum. Any remaining radioactivity was treated as part of background and was subtracted from total Geiger-Müller tube radioactivity. Results In 7 of the 61 patients tested, the P32 uptake over the nodule was increased by 20 per cent or more, which was considered a positive test for cancer. The range of increase was from 23 to 61 per cent. In the remaining 54 patients the test was negative, with increases of P32 uptake of 12 per cent or less (12 to minus 22 per cent), except for 1 case with a 16 per cent increase. Of the group of 54 patients with negative tests, 32 were subsequently operated upon and tissue diagnoses were obtained (Table I). On microscopic section almost all the lesions proved to be benign adenomas. Three patients had hyperthyroid nodules and 1 had a thyroglossal duct cyst.