Secondary or Second Primary Malignancy in the Thyroid? Metastatic Tumors Suggested Clinically: A Differential Diagnostic Task

Abstract

Objective: To describe the algorithms employed to explore the suggestion or consideration of metastatic malignancy in the thyroid. Study Design: Thirty-seven cases with a history of malignancy (n = 21) and/or uncommon fine-needle aspiration biopsy (FNAB) findings (n = 37) were reviewed and reclassified according to The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). Results: The group was heterogeneous in terms of the final histopathology results: the suggested metastasis was confirmed in only half of the cases (11/21; 52.4%). Primary thyroid malignancies were mostly nondifferentiated, medullary, or rare. However, 3 papillary carcinomas (the less common variants) were also found. Finally, 5 out of 37 cases were surprisingly benign upon histopathological investigation (uncommon repair and fibrotizing Hashimoto thyroiditis). Conclusions: The metastatic nature of thyroid gland nodule(s) must be considered in cases of generalization of malignancy and/or uncommon FNAB findings. We must be as open-minded as possible from the outset. Additional techniques are helpful if available - cytoblock and immunocytochemistry can contribute substantially. Morphological comparisons with the previous malignancy are recommended whenever possible. To avoid overtreatment, cases without precise typing should not be classified as TBSRTC diagnostic category VI - malignant, but should remain in TBSRTC diagnostic category V - suspicious for malignancy. Repeated FNAB to enable additional techniques may be suggested.

Fine‐needle aspiration biopsy of secondary neoplasms of the thyroid gland: A multi‐institutional study of 62 cases

“…On the basis of histologic data, cytologic case reports, and small FNAB series, there is an SNTG subset that exhibits morphologic features overlapping with those of primary thyroid carcinomas, including PTC, follicular thyroid carcinoma, medullary thyroid carcinoma, PDTC, and UTC, and, thus, constitutes a potential pitfall in cytologic evaluation . Clearly, a major challenge in the diagnosis of SNTG is related to the wide variety of histologic types and primary tumor origins that can be encountered.…”

“…In contrast to AdCC, PTC with an adenoid cystic pattern exhibits the classic nuclear features of PTC rather than hyperchromatic nuclei. Furthermore, ancillary markers for AdCC, including thyroglobulin, PAX‐8, and TTF‐1 for PTC, and CD117, and MYB, can be useful …”

“…On the basis of histologic data, cytologic case reports, and small FNAB series, there is an SNTG subset that exhibits morphologic features overlapping with those of primary thyroid carcinomas, including PTC, follicular thyroid carcinoma, medullary thyroid carcinoma, PDTC, and UTC, and, thus, constitutes a potential pitfall in cytologic evaluation. 24,26,32,[50][51][52][53][54][55][56] Clearly, a major challenge in the diagnosis of SNTG is related to the wide variety of histologic types and primary tumor origins that can be encountered. In addition, the diagnosis of SNTG by FNAB can be made more difficult by a lack of clinical history indicating an extrathyroid cancer or by a long lag time between primary diagnosis and the development of an SNTG.…”

“…Furthermore, ancillary markers for AdCC, including thyroglobulin, PAX-8, and TTF-1 for PTC, and CD117, and MYB, can be useful. 51,52,70 Molecular Studies for the Diagnosis of SNTG in FNAB To our knowledge, the value of gene expression classifier tests like Afirma (Veracyte, South San Francisco, Calif) as an ancillary test for diagnosing SNTG in thyroid FNAB has not been evaluated to date. It is noteworrhy that, in 1 of our cases of RCC that was diagnosed as malignant, an Afirma test was performed and was reported as "suspicious" with a comment that the genetic signature identified was similar to that observed in RCC.…”

Thyroid Malignancy Risk of Incidental Thyroid Nodules in Patients with Non-Thyroid Cancer

“…Nevertheless, the frequency of thyroid cancer in incidentally found thyroid nodules in these patients is still not fully known. As far as we know, there are a limited number of studies on the prevalence of primary thyroid cancer in non-thyroid cancer patients in the literature (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”