A rare instance of so-called primary thyroid tumor of the head of the humerus is reported. On gross and histological examination, the growth resembled a benign adenoma of the thyroid gland. Biological assay with extracts of the tumor showed that it contained a substance which would cause metamorphosis in tadpoles and, when fed to mice, would decrease the toxicity of acetonitrile for these animals; these findings strongly suggested that the tumor contained thyroid hormone.
Amputation failed to effect a cure, and, three and one-half years after disarticulation of the arm at the shoulder, a massive growth recurred. Signs and symptoms of a very acute thyrotoxicosis developed, from which the patient died. Histological examination of the tumor at this time showed it to be much more undifferentiated than the original growth. At no time throughout the entire period of observation until shortly before the patient's death was there any evidence of a growth in the thyroid. At this late date, a very slight lobulation of the gland was palpable, although it was not enlarged and was freely movable.