A 75-year-old woman presented in February 1989 with a multinodular goiter with functional autonomy. Her past history included a left hemicolectomy in July 1987 for a Dukes’ C sigmoid cancer with a preoperative carcinoembryonic antigen (CEA) level of 1 ng/mL. She had no clinical signs of hyperthyroidism other than palpitations. On physical examination no thyroid enlargement was detected. Ultrasound showed a symmetric multinodular substernal goiter of approximately 131 g with a heterogenic tracer fixation on thyroid scintigraphy. Hyperthyroidism was successfully controlled with thiamazole. Thyroid scintigraphies performed in 1990 and 1992 (Fig 1A) showed no dominant cold nodules.

In 1991 a CA 19-9 level of 94 U/mL was coincidentally measured. Abdominal ultrasonography and computed tomography (CT) scan showed no liver metastasis, no local relapse of the sigmoid carcinoma, and no pancreatic or bile duct abnormalities. Colonoscopy and gastroscopy were normal. CA 19-9 continuously increased to 620 U/mL in 1992, 890 U/mL in 1993, and 1,020 U/mL in September 1994. Meanwhile, CEA climbed from 4.1 to 21 ng/mL. During these 2.5 years, the patient underwent four CT scans of the abdomen and pelvis, three chest x-rays, two CT scans of the thorax, a CT scan of the brain, a bone scintigraphy, three colonoscopies, a double-contrast barium enema, a gastroscopy, and an endoscopic retrograde cholangiopancreatography in a fruitless search for the origin of the increasing CA 19-9 level.

In August 1994, the patient complained of exertional dyspnea, dyspnea while bending, and mild dysphagia. On examination, jugular vein distention was visible along with thyroid enlargement. X-rays showed tracheal compression with a clinical relevant repercussion on flow-volume loop. CT scan and ultrasound showed enlargement of the multinodular goiter with a hypoechogenic nodule of approximately 5 cm in diameter in the left lobe and significant substernal extension. On thyroid scintigraphy (Fig 1B), an enlargement of 175 g with the development of a large cold nodule in the left lobe and a smaller one in the lower third of the right lobe was noted. A total thyroidectomy was performed and revealed a 8.5 × 6 × 5 cm³ metastasis of a well-differentiated adenocarcinoma of intestinal origin in the left lobe near the resection margin. Two months later, CA 19-9 was reduced to 151 U/mL and CEA to 4 ng/mL.

In January 1995, relapse occurred in the thyroid (CT scan, Fig 2) that was treated by incomplete resection and postoperative radiotherapy. An extensive evaluation revealed no other metastases. The patient died in September 1995 from local massive tumor growth in the neck region leading to suffocation.

Although thyroid metastases are uncommon in clinical practice, autopsy data shows a high rate of subclinical involvement. An autopsy study of 1,980 consecutive patients dying with malignancy found 9.5% to have thyroid metastases after meticulous postmortem examination of the thyroid gland. The greatest incidence was for malignant melanoma (39%), followed by carcinoma of the breast (21%), kidney (12%), and lung (11%). Only 5% of these thyroid metastases were described as a thyroidal mass or enlargement in the clinical record.¹ It may be that clinical involvement of the thyroid gland is infrequently sought for and often appears overshadowed by the classic sites where metastases are found. Renal cell carcinoma is by far the most frequent source of thyroid metastases in clinical series.^2,3 Presentation of an asymptomatic mass, normal thyroid functions, and a cold nodule on thyroid scintigraphy can occur months to years after treatment of a primary cancer and thus often produces a clinical dilemma.^4,5 Workup should include ruling out other metastatic cancers and fine-needle aspiration cytology of the suspected thyroid mass.^3,6 If isolated metastatic cancer to the thyroid is found, surgical resection should be performed, because it often prolongs disease-free survival and occasionally may be curative.^3-5

The reported case posed a persistent diagnostic problem. Increase in CA 19-9 in a patient with a history of colon cancer is most likely due to a local relapse or development of distant metastasis. Both possibilities as well as other known reasons⁷ for increasing CA 19-9 were extensively examined during a 4-year period, thereby not considering a multinodular goiter without a dominant cold nodule (Fig 1A) to be the site of metastatic disease. We believe that this is the first reported case of a thyroid metastasis from colorectal cancer in the absence of lung or liver metastasis. Thus a new thyroid mass in a patient with a previous history of malignancy should be considered to be secondary thyroid cancer until proven otherwise.