Tumors metastatic to thyroid neoplasms: a case report and review of the literature

Abstract

Metastasis into a thyroid neoplasm-tumor-to-tumor metastasis-is exceedingly rare. We describe the 28th documented case of a tumor metastatic to a thyroid neoplasm and review the literature on tumor-to-tumor metastasis involving a thyroid neoplasm as recipient. All cases showed a recipient thyroid neoplasm with an abrupt transition to a morphologically distinct neoplasm. Metastasis into primary thyroid neoplasm was synchronous in 33% of cases and metachronous in 67%. Follicular adenoma was the most common recipient thyroid neoplasm overall (16/28), and papillary thyroid carcinoma was the most common malignant recipient neoplasm (9/28). Of the 9 recipient papillary carcinomas, 6 were follicular variants. Renal cell carcinoma was the most common neoplasm to metastasize to a primary thyroid neoplasm (9/28), followed by lung (6/28), breast (5/28), and colon (3/28) carcinoma. Tumor-to-tumor metastasis should be considered whenever a dimorphic pattern is encountered in a thyroid tumor.

Figure 1

(a) Low power (20x; H & E) photomicrograph demonstrating invasive lung tumor arranged in nests and islands with abundant central necrosis. Cytologically (b) the malignant cells displayed enlarged, hyperchromatic nuclei with vesicular to coarse chromatin and a moderate amount of amphophilic cytoplasm (200x; H & E).

Figure 2

(a) An encapsulated tan-brown adenoma was present within the right thyroid lobe with multifocal white-tan areas within the adenoma (arrows). Within the encapsulated follicular adenoma is an abrupt transition to a morphologically distinct neoplasm (asterisk) (40x; H & E) (b). Metastatic carcinoma (asterisk) was arranged in nests with enlarged vesicular nuclei with inconspicuous nucleoli infiltrating the follicular adenoma (200x; H & E) (c). The metastatic carcinoma was negative for thyroglobulin, while the adenoma was strongly positive (100x; IHC) (d).