A case report of anaplastic thyroid cancer and papillary thyroid cancer lymph node metastasis: an unusual presentation as an invasive hypopharyngeal mass.

Anaplastic thyroid carcinoma is a rare undifferentiated tumour of the thyroid follicular epithelium. It almost always develops from a pre-existing well-differentiated thyroid cancer with a co-existent thyroid malignancy varying from 5 to 17% . The co-existence of papillary thyroid cancer (PTC) with anaplastic thyroid cancer is a rare occurrence in metastases outside the primary thyroid lesion. Traditionally, this has been regarded as an aggressive form of cancer associated with a dismal prognosis. Recently, the focus has shifted to the development of novel therapies based on the availability of comprehensive genomic profiling platforms (CGP) with a rapid turn-around to identify molecular aberrations in tumours which acts as potential therapeutic targets. In the United Kingdom, we report the case of a 60-year-old woman with an unusual presentation of (metastatic) anaplastic thyroid carcinoma and concomitant papillary thyroid cancer metastasis within a contralateral lymph node. This was initially perceived as a left pyriform fossa mass involving and compressing her left hemi-larynx on clinical and radiological examination. Following the identification of BRAF V600E mutation on CGP, she was started on targeted therapy with the BRAF inhibitor dabrafenib and the MEK inhibitor trametinib and demonstrated excellent clinical and radiological response following 7 months of treatment. She has subsequently undergone total thyroidectomy alongside with bilateral neck dissection, and is due to start radioactive iodine treatment to reduce the risk of recurrence of disease.