title: 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.
authors.affiliation: Department of Pathology, Creighton University Medical Center, Omaha, NE 68131, USA.
authors.forename: Todd M
authors.initials: TM
authors.lastname: Stevens
authors.forename: Alan T
authors.initials: AT
authors.lastname: Richards
authors.forename: Chhanda
authors.initials: C
authors.lastname: Bewtra
authors.forename: Poonam
authors.initials: P
authors.lastname: Sharma