Undifferentiated Thyroid Carcinoma With Anaplastic Features in a 78-Year-Old Filipino Female: A Case Report

Background: Anaplastic thyroid carcinoma (ATC) accounts for 0.8-9.8% of all thyroid cancers globally with a median survival from diagnosis of 5 months. Clinical Case: A 78-year-old Filipino female sought consult due to a rapidly progressive anterior neck mass. This started as a centimeter-sized nodule initially noted three months prior. Two months after, there was gradual enlargement to a fist-size, movable mass, hard in consistency associated with dysphagia and hoarseness of voice. On consult, neck ultrasound revealed an enlarged right thyroid with a mass in the right lobe (TI-RADS 5), multinodular with no lymphadenopathy. Furthermore, a CT scan of the neck was done to evaluate for other structural causes of dysphagia showing no intrathoracic extension. Patient was advised surgery but was lost to follow up due to lockdown from COVID-19. In the interim, patient was admitted for aspiration pneumonia. IV antibiotics were initiated and urgent surgery was advised to relieve patient of respiratory compromise. Patient was airlifted to a tertiary care center for further management. Baseline thyroid function tests were normal. Repeat neck imaging showed interval increase in the hypodense mass measuring 6x9x8 cm (from 3x4x5 cm) (APxWxCC) extending to the hypopharynx and laryngeal vestibule with mass effect to the trachea and esophagus. A multidisciplinary meeting was done to establish goals of care. On the 3rd hospital day, a tracheostomy with incisional biopsy and frozen section was done which revealed round to spindle cell neoplasm with anaplastic features. No further surgical resection was done and specimen was sent for immunohistochemical staining. Long term enteral access was secured during the same operation. Final histopathology showed undifferentiated thyroid carcinoma with anaplastic features and no definite lymphovascular invasion. Immunohistochemical markers were negative for CD3, CD20, Thyroglobulin, TTF-1, PAX8, Calcitonin and Pancytokeratin which reveal loss of tumor antigenicity, consistent with the histopathologic diagnosis. Metastatic work-up revealed varisized pulmonary, subpleural and hepatic nodules with lymphangitic carcinomatosis. Patient was staged as IVC (T4N1M1). Patient was referred for radiation to maximize local control, to complete 33 fractions of 200 cGy on the thyroid mass and received one cycle of Paclitaxel before discharge. Concurrent chemoradiation was continued and completed 29 cycles of radiation and 2 cycles of Paclitaxel which significantly reduced the tumor size. However, the patient succumbed to acute coronary syndrome on her third admission. Conclusion: There is currently no consensus first-line treatment modality available worldwide. Although the diagnosis and treatment of ATC is considered medically urgent, end-of-life planning must be given high priority in order to optimize the quality of the patient’s remaining life.

Anaplastic Thyroid Carcinoma Histologically Mimicking a Plasmacytoma

Anaplastic (undifferentiated) thyroid carcinoma (ATC) is a rare malignancy which may arise from transformation of a pre-existing differentiated carcinoma. We report the unique case where a lesion of thyroid origin presented with the histological features of mature plasma cells. Immunohistochemistry confirmed the lesion to be an anaplastic thyroid carcinoma arising from papillary thyroid carcinoma. A tumor mimicking a malignancy of a different cellular origin can lead clinicians to incorrect treatment approaches. Careful correlation with clinical details and knowledge of these unique presentations is important for reaching the correct diagnosis.