Abstract
RATIONALE: Anaplastic thyroid carcinoma (ATC) is a rare highly aggressive thyroid malignancy. Thyroid sclerosing mucoepidermoid carcinoma with eosinophilia is also a rare low grade malignant thyroid neoplasm. To date, comorbidity of these 2 tumors in the thyroid gland has not been reported in the English literature. PATIENT CONCERNS: Here, we present a case of a 67-year-old women with a 6-month history of mass of left neck. She complained of a painless mass in the right neck. DIAGNOSES: Based on histopathological examination of H&E stained sections, immunohistochemical staining assay and molecular tests, the patient was diagnosed with ATC combined with sclerosing mucoepidermoid carcinoma with eosinophilia. INTERVENTIONS: The patient underwent radical surgery for thyroid cancer. OUTCOMES: No complications, local recurrence or metastases were observed during a 1 year and 3 months follow-up after surgery. LESSONS: To the best of our knowledge, this is the first case report on ATC combined with sclerosing mucoepidermoid carcinoma with eosinophilia in the English literature. This condition can be easily misdiagnosed during thyroid fine needle cytology. Clinicians should perform morphological examination, immunohistochemistry and molecular tests on resected specimen to make a definitive diagnosis.