Jornal de Distúrbios e Terapia da Tireóide
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Involvement of Parathyroid Glands by Differentiated Thyroid Cancers and its Influence on Treatment Outcome

Khalid Hussain AL-Qahtani, Mushabbab Al Asiri, Mutahir A. Tunio, Naji J Aljohani, Yasser Bayoumi, and Khalid Riaz

Background: Parathyroid gland (PTG) involvement by differentiated thyroid cancer (DTC) patients is rare and its influence on disease outcome has been less studied. We aimed to evaluate the frequency and patterns of PTG involvement in DTC patients and to evaluate the influence of PTG infiltration by DTC on treatment outcome in our cohort. Methods: Demographic, clinicopathologic characteristics and treatment outcomes of sixteen patients of PTG involvement were reviewed in a series of consecutive 823 DTC patients treated during July 2001 and December 2012 with thyroidectomy followed by radioactive iodine therapy and radiation therapy. Data regarding the occurrence of locoregional recurrence (LRC) or distant metastasis (DM), disease free survival (DFS) and overall survival (OS) rates were recorded. LRC, DMC, DFS and OS rates were also compared to matched controls (T3, T4a and M1) using the log-rank test. Results: Mean age of cohort was 57.5 years (42.9-72.1) with female gender preponderance (75%). Sixteen cases of DTC with PTG involvement were found among the 823 patients (1.94%). Fourteen cases (87.5%) had direct extrathyroid extension (ETE) to PTG and 2 (12.5%) had metastatic foci. Majority of involved PTG were located within the thyroid capsule (intracapsular) (50%). PTG involvement was associated with extrathyroidal extension in 13 cases (81.3%). Median size of primary thyroid cancer was 3 cm (2.2-5.4). Fourteen patients (87.5%) with PTG involvement had positive cervical lymph nodes and 12 patients (75%) had lymphovascular space invasion. At 5 years, LRR, DMC, DFS and OS rates were 87.1%, 66.3%, 64.3% and 58.3% respectively. DTC patients with PTG involvement had similar DFS as compared to pT4a (62.5% vs. 60.4%: p 0.08). Conclusion: PTG involvement in DTC patients is rare and is associated with older age, advanced stage and with ETE. In the presence of ETE, PTG involvement can be high.