Background: Metastases to thyroid (TM) are rarely observed in the clinical practice.
Objective: To assess the prevalence, clinicopathological aspects and prognosis of TM, and to evaluate the role of thyroidectomy in the management of TM.
Methods: The pathology files (databases) of two Italian Pathology Units were searched for thyroid cytology (FNAC) and histology reports covering the time period January 1993 through December 2003.
Results: Thirty-six cases of TM were found, accounting for 0.13% of thyroidectomies and 0.07% of FNAC. The main site of origin of TM was the lung, followed by oesophagus, breast and kidney. TM patients were divided into two groups, based on whether they were (Group 1) or were not (Group 2) submitted to surgery. Thirty-five subjects diagnosed with the same primary tumours as TM patients, but without TM, served as controls. The mean patient age, the mean time from diagnosis of primary tumour to TM detection, and the mean survival time did not significantly differ in Group 1 and Group 2 (63.2 +/- 1.6 vs. 66.6 +/- 2.9 years, 24.7 +/- 8.6 vs. 19.7 +/- 4.4 months and 24.3 +/- 4.9 vs. 39 +/- 9.9 months, respectively). In contrast, the mean time from detection of TM to death was longer in Group 1 than in Group 2 (14.3 +/- 2.5 vs. 4.5 +/- 0.5 months, respectively; P = 0.002). The overall survival of TM patients and control subjects was not significantly different (33.7 +/- 6.6 vs. 32.3 +/- 6 months).
Conclusions: TM is a rare event, is more frequent in patients older than 60 years, and has the same impact on prognosis as nonthyroidal metastases. Although thyroidectomy may be useful to avoid further dissemination of the primary tumour in case of solitary TM, it does not contribute to prolonging patient's life.