Metastatic Colon Carcinoma in a Preexisting Thyroid Nodule

Dear Editor:

Metastases to the thyroid is a clinically uncommon disease entity, with an incidence of 1.9%–24% in autopsy series (1). Although kidney, breast, and lung metastases to the thyroid are not unusual, metastasis from colon cancer is rare. Here we describe a patient with metastatic carcinoma of the thyroid from colon cancer in whom, unlike previous reports, the lesion developed in an already existing thyroid nodule.

A 59-year-old woman had surgery and chemotherapy for moderately differentiated adenocarcinoma of the ascending colon. Chest computed tomography (CT) after 6 months revealed two nodules in the right lung, which were colon carcinoma metastases, as revealed by wedge resection, as well as multiple thyroid nodules with hypoattenuation. The largest was in the right thyroid. On ultrasound (US) the nodule was isoechoic, 3.7 cm with well-defined margins, wider-than-tall shape, and no calcifications. This mass did not show up on positron emission tomography with CT (PET-CT).

Contrast-enhanced CT scans obtained from PET-CT performed 1 year later revealed a newly developed hypoattenuating nodule within the previously detected mass and this area had intense fluorodeoxyglucose uptake on PET scan (Supplementary Fig. S1; Supplementary Data are available online at www.liebertonline.com/thy). US showed a 4.2-cm mass with a 1.9-cm hypoechoic solid component within the mass (Supplementary Fig. S2). The patient had also developed a 0.7-cm nodule with intense fluorodeoxyglucose uptake at the resection margin of right upper lung lobe on the same PET-CT scan, suggesting recurred lung metastasis. US-guided fine-needle aspiration biopsy (US-FNAB) of the thyroid was performed targeting the newly developed hypoechoic area within the mass, and malignant cells of nonthyroid origin, favoring metastatic carcinoma, were noted on cytology. Additional US-FNAB was performed targeting at the isoechoic preexisting mass, and benign clusters of follicular cells were observed on cytology. The patient is now under chemotherapy. Thyroid surgery was not performed as there were widespread metastases.

Metastatic carcinoma to the thyroid may occur preferentially in multinodular goiter (2,3). We are not aware, however, of reports of metastasis within a preexisting thyroid nodule. Imaging studies are of limited value as features suggestive of both benign and malignant thyroid nodules can be seen. Absence of microcalcifications in lesions with suspicious US features may be suggestive of metastatic nodules in patients with a known history of nonthyroidal cancer (4). As in most other thyroid nodules, US-FNAB is quite useful in identifying a malignant lesion. As illustrated by this patient, sometimes solitary thyroid nodules that are apparently homogeneous on palpation are not so and may contain more than one lesion, emphasizing the importance of US and US-FNAB in their evaluation.