SUN-393 - Sclerosing Mucoepidermoid Carcinoma with Eosinophilia: A Rare Case of Primary Thyroid Cancer

Background: Sclerosing mucoepidermoid carcinoma with eosinophilia (SMECE) is a very rare primary thyroid cancer. SMECE was first described in 1991 by Chan et al., and fewer than one-hundred cases have been reported. Given the limited number of cases, there exist no guidelines for diagnosis nor for management.

Case Presentation: A forty-six-year-old female with Hashimoto's thyroiditis and hypertension originally presented for evaluation of worsening anterior neck swelling, chronic cough, and dyspnea on exertion. Initially, a thyroid ultrasound revealed a multinodular goiter with a dominant 7.5 cm right sided TR4 nodule and abnormal cervical lymph nodes, the largest measuring up to 2.9 cm. CT of the neck showed thyroid enlargement, tracheal narrowing and right sided lateral neck lymph nodes. Fine-needle aspiration of the right supraclavicular lymph node demonstrated metastatic mucoepidermoid carcinoma.
She underwent total thyroidectomy and radical right neck dissection, complicated by damage to bilateral recurrent laryngeal nerves requiring tracheostomy and post-operative hypoparathyroidism. Surgical pathology of her thyroid and left paratracheal tissue showed sclerosing mucoepidermoid carcinoma with eosinophilia and tumor involvement in bilateral thyroid lobes and in the isthmus. Four out of thirty-two lymph nodes were positive for metastatic carcinoma with extrathyroidal extension, extranodal extension, and lymphovascular invasion on surgical pathology.

Discussion: SMECE is an uncommon form of primary thyroid cancer. It is often associated with Hashimoto's thyroiditis and predominantly presents in middle-aged females. Characteristic histopathologic features include nests of epidermoid and mucinous cells with stromal sclerosis and eosinophilia, typically arising in the background of chronic lymphocytic thyroiditis.
Although it is a low-grade malignancy, SMECE often demonstrates locally aggressive behavior, including lymph node metastases, extrathyroidal extension, and extranodal spread. Though there are no established treatment guidelines, the primary therapeutic approach centers around surgical resection. Due to its rarity, recognition of SMECE carries important clinical implications for endocrinologists given its potential for recurrence and metastases, underscoring the need for long-term surveillance.

Conclusion: We describe the rare presentation of a primary thyroid cancer with pathology expressing sclerosing mucoepidermoid carcinoma with eosinophilia.

Reference:
1. Chan JK, Albores-Saavedra J, Battifora H, Carcangiu ML, Rosai J. Sclerosing mucoepidermoid thyroid carcinoma with eosinophilia. A distinctive low-grade malignancy arising from the metaplastic follicles of Hashimoto’s thyroiditis. Am J Surg Pathol 1991;15(5):438–48. Doi: https://doi.org/10.1097/00000478-199105000-00003

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