To the Editor.— The clinical situation of an enlarging, clinically significant thyroid mass in a patient with a known cancer presents a challenge in diagnosis. The presentation, diagnostic investigations, and outcome in this case were unusual. Report of a Case.— A 68-year-old man had an adenocarcinoma of the sigmoid colon surgically removed in 1967. On May 11, 1971, he was seen at the Thomas Jefferson University Hospital with hoarseness, cough, dysphagia, weight loss, and a painless anterior neck mass of increasing size. The large, homogeneous, firm, nontender, cool mass is shown in the Figure. The patient was clinically and chemically euthyroid. The chest x-ray film demonstrated tracheal deviation. A thyroid scan gave normal findings with no radioactivity detected in the clinically palpable mass. Because of biopsy-proven liver metastases and the patient's poor general condition, a percutaneous Vim-Silverman needle biopsy of the mass was done. Thyroid tissue obtained contained metastatic colonic