Role of fine-needle aspiration cytology in the diagnosis of secondary tumors of the thyroid—twenty years' experience

Abstract

Secondary tumors of the thyroid, presenting as thyroid nodules although rare, have been documented in literature. This study highlights the frequency, primary sites, and the role of fine-needle aspiration cytology (FNAC) in evaluating secondary tumors of the thyroid at a tertiary care hospital. There were 24 documented cases of secondary tumors of the thyroid from 1982 to 2002 (20 years). The aspirates and histology slides of all these cases were reviewed and the findings noted. On FNAC, 17 cases were diagnosed as secondary tumors, 3 as primary, and in 4 cases it was difficult to categorize the tumors as either primary or secondary. In 12 out of 24 cases, the primary tumor was seen to arise in the larynx (9), and in other sites anatomically close to the thyroid including the trachea (1), and the esophagus (2). Metastases from distant organs were also observed. Secondary tumors of the thyroid are rare and should be suspected in patients when the FNAC shows cytological features not seen in primary thyroid tumors. FNAC alone was required to accurately diagnose secondary tumors of the thyroid in a majority of cases (17/24); however, in some cases ancillary techniques may be required for a definite diagnosis.

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“…Oncological patients represented only 6.3% of that population, in contrast to centres specialising in the diagnosis and treatment of cancers that present many reports on metastases to the thyroid gland [13,[27][28]. Probably for this reason, in our study the percentage of patients with secondary cancer (0.3%) was lower than in typical oncological centres, and similar to that found in centres involved in the diagnosis of thyroid disorders [15,25] and in general centres (non-specialised) [8] (Table IV). Regardless of that fact, our data showed regularity in higher risk of metastasis in patients with malignant disease than in those with negative history of cancer.…”

“…But this explanation is not complete as the percentage of males among patients with metastases of those tumours was two-times higher than that among all the patients with these tumours subjected to FNA (Table I). Similarly, in other studies [14,17,28,30] males constituted 40%-50% and even more than 70% [15] of patients with metastasis to the thyroid gland. It should also be stressed that the percentage of males among patients with secondary thyroid tumours was much higher than the percentage of males among patients with primary thyroid cancers, which in our data was 11% [31].…”

“…After taking into account the relative frequency of metastases (in relation to the number of patients subjected to FNA with a specific cancer) we observed that the dominant type of metastases was a tumour infiltrating the thyroid by direct extension from the neighbouring primary lesion. Also other authors showed that tumours of the head and the neck were the most common [14][15] or frequent [8] source of metastasis. However, most of the authors limited their analyses to metastases from distant organs only.…”

“…Similarly, other authors indicate that FNA did not always accurately diagnose metastatic disease, but it identified a thyroid malignancy in approximately 90% of cases [8,[14][15][37][38][39]. Clinical data about the occurrence of cancer in a patient can help in precise cytological diagnosis [14,25].…”

“…Metastases to the thyroid are revealed clinically with a frequency of 0.1-3% in patients diagnosed or operated for thyroid nodules/cancer [1,[7][8][9][10][11][12][13][14][15][16]. Hegerova et al found metastases in 97 out of 10,798 (0.9%) patients identified from a database of cytological material archived over 30 years at the Mayo Clinic [17].…”