[Diagnosis of metastasis of malignant melanoma in the thyroid gland with f18-FDG PET scan]

Metastatic carcinoma to the thyroid gland: a single institution 20-year experience and review of the literature

The thyroid gland is an uncommon site for metastatic disease but cases have been well-documented in the literature, particularly in autopsy series. A retrospective review of surgical pathology and autopsy pathology database for patients with metastatic carcinoma to the thyroid was performed at the University of Massachusetts Medical Center between January 1993 to January 2013. We identified a total of 10 patients with metastatic carcinoma to the thyroid; 6 were in surgical pathology specimens out of a total of 1,295 thyroid carcinoma (0.46 %) and 4 were diagnosed at autopsy out of a total of 2,117 (0.19 %) autopsy cases during this period. Cases with direct extension of the tumor into the thyroid from local primary sites such as larynx, esophagus or soft tissues of the neck were excluded. The primary tumors in these cases comprised of four lung carcinomas, three colorectal carcinomas, a renal cell carcinoma, a pleural malignant mesothelioma, and an unknown primary. Therefore, it is important to keep intrathyroidal metastases in the differential diagnosis when evaluating a thyroid nodule, particularly in patients with a previous history of malignancy. Furthermore, a literature review reveals over 1,400 cases have been previously reported, with the most common malignancies from the kidney (34 %), lung (15 %), gastrointestinal tract (14 %), and breast (14 %).

Isolated metastasis of malignant melanoma into follicular carcinoma of the thyroid gland

A 38-yr-old woman with a history of malignant melanoma (MM) presented with a thyroidal nodule. Fine needle aspiration biopsy of the thyroid was consistent with metastatic MM. The patient underwent thyroidectomy: microscopic examination revealed a follicular carcinoma nodule harboring a focus of metastatic melanoma. On review of the fine needle aspiration biopsy specimen, the population of cells with more uniform nuclei with focal follicle formation, which initially was interpreted as cells originating from normal thyroid tissue, was seen to actually represent the follicular carcinoma component. Tumor-to-tumor metastasis is an interesting phenomenon and there are only few cases of MM metastasis to other tumors. MM metastasis into a neoplastic thyroid nodule is a very rare combination and may be explained because the nodule in question represents the most highly vascularized component of the thyroid.

The natural course of cutaneous melanoma

The natural course of cutaneous melanoma (CM) is determined by its metastatic spread and depends on tumor thickness, ulceration, gender, localization, and the histologic subtype of the primary tumor. CM metastasis develops via three main metastatic pathways and occurs as satellite or in-transit metastasis, as regional lymph node metastasis or as distant metastasis at the time of primary recurrence. About 50% of all CM patients with tumor progression firstly develop regional lymph node metastases. In the other 50% the first metastases are satellite or in-transit metastases (about 20%), or immediately distant metastases (about 30%). Development of distant metastasis appears to be an early event in metastatic spread and may in the majority of cases originate from the primary tumor, only few cases may develop secondarily to locoregional metastasis. Reporting of organ involvement in distant metastasis greatly differs between the results of imaging techniques and autopsy results in respect to the metastatic patterns detected, pointing out that there is a need of improved imaging systems. Proliferation, neovascularization, lymphangiogenesis, invasion, circulation, and embolism are important steps in the pathogenesis of CM metastasis, with tumor vascularity as an important independent significant prognostic factor. The expression of chemokine receptors in cancer cells associated with the expression of the respective chemokine receptor ligands in the target sites of the metastasis is an interesting observation which may stimulate the development of new therapeutic strategies.