Clear Cell Variant of Papillary Thyroid Carcinoma With Associated Anaplastic Thyroid Carcinoma: Description of an Extraordinary Case

Clear cell change is a rare observation in thyroid cancer, resulting from aberrant cytoplasmic accumulation of lipids, glycogen, or thyroglobulin in the tumor cells. The phenomenon is most common for follicular thyroid neoplasia, with no definite coupling to patient outcome. The clear cell variant of papillary thyroid carcinoma (ccPTC) is even more infrequent—making conclusions regarding prognosis difficult. Single reports describe distant metastases of ccPTCs as well as co-occurrence with anaplastic thyroid carcinoma (ATC). In this report, a case of a therapy-resistant ccPTC dedifferentiating into an ATC is characterized from morphological and immunohistochemical standpoints. The patient was a 79-year-old female presenting with a 45-mm nodule in her right thyroid lobe. A first round of cytology raised the suspicion of PTC, but a repeated biopsy verified an ATC diagnosis. Neoadjuvant doxorubicin and external irradiation therapy was administered, and the patient developed lung metastases concomitantly. A palliative lobectomy was performed, and the final diagnosis was a ccPTC with focal dedifferentiation into an ATC. Intriguingly, the ccPTC component was viable and dominated the lesion. The clear cell morphology stemmed from an accumulation of glycogen, while the anaplastic component was devoid of evident clear cell changes. The case is one of exceedingly few descriptions of a ccPTC that dedifferentiates to an ATC, suggesting that this PTC subtype is not without potential for development of a highly lethal tumor component. Moreover, the partial lack of response to neoadjuvant therapy suggests a possible underlying resistance to aggressive treatment modalities in this particular case.