Parathyroid Involvement by Thyroid Carcinoma: Results from a Single Institution and a Review of the Literature

Thyroid cancer (TC) is a common malignancy that accounts for approximately 1% of all human cancers. Given their anatomical proximity to the thyroid, the parathyroid glands (PTG) are theoretically at risk of tumor involvement. However, PTG metastases are rare and may be underdiagnosed because of routine PTG preservation during thyroidectomy. This study aimed to identify cases of PTG invasion by TC through a 10-year retrospective review at Chosun University Hospital, along with an analysis of the existing literature. Among 1,032 thyroidectomies, PTG involvement was detected in 10 cases (0.97%). The affected patients included nine females and one male, with a mean age of 46 years (range: 25-77 years). Histological examination confirmed papillary thyroid carcinoma (PTC) in all cases. Tumor invasion into the perithyroid soft tissues was observed in nine patients, and central cervical lymph nodes metastases were present in four. All patients exhibited PTG pattern A (direct invasion). Based on our findings and literature data, PTG involvement by TC has an incidence rate of 0.05–3.9%, predominantly affects women in their sixth to seventh decade of life, and appears to no impact on prognosis unless accompanied by extensive extrathyroidal invasion. Further studies are necessary to determine whether PTG invasion should be integrated into the TNM staging system and to assess its prognostic and therapeutic implications.