SAT554 Follicular Variant of PTCA Initially Presenting with Widespread Metastases

Disclosure: N.N. Bisquera: None. R.C. Mirasol: None. Background: Papillary thyroid carcinoma accounts for most cases of thyroid cancer. Most cases of PTC have a good prognosis and low incidence of metastases. The follicular variant is the most common variant. First described in the 1960’s, the understanding of FV-PTC began to evolve with molecular profiling demonstrating a similarity with FTC, and clinical behavior profiling showing that a subtype may behave like PTC with a propensity for lymph node metastases. We are presented with an unusual case of an infiltrative FV-PTC presenting with widespread multiple metastases on diagnosis. Clinical Case: A 64-year-old female, presented with 1-year history of a slowly enlarging mass on the left mandible, which was also associated with an enlarging anterior neck mass. She had no constitutional symptoms and had previously been in good health. On examination, there was a 7x8x3 cm hard, fixed left mandibular mass. There was also a palpable right thyroid nodule measuring 2.5x2 cm. There was no difficulty in swallowing or breathing, but she had some difficulty in eating due to trismus. There were no associated symptoms of hypo/hyperthyroidism. Investigations revealed a euthyroid status. CT scan showed a solid lobulated heterogeneously enhancing mass measuring 4.2x5.1x5.2cm on the body and angle of the left mandible. Ultrasound showed multiple thyroid nodules, the largest - a mixed cystic and solid mass measuring 2.9 x 2.7 x 2.17 cm on the right thyroid lobe, for which FNA was performed. Histopathology showed benign follicular nodules. Incision biopsy of the mandibular mass showed presence of thyroid tissue. Further imaging showed metastases to the left frontal, parietal bone, T7 vertebra, and bilateral lungs. The case was discussed in a multi-disciplinary tumor board meeting. With a pre-operative diagnosis of a primary thyroid malignancy, the patient then underwent a total thyroidectomy with segmental mandibulectomy. Post-operative histopathology showed a metastatic multifocal infiltrative follicular variant of PTC. RAI was administered post-surgery, and she was started on suppressive thyroxine therapy. Steroids were given during RAI, with no untoward events post treatment. Post-ablative whole body scanning revealed increased tracer uptake in multiple areas: left frontal and parietal bone, bilateral thyroidal beds, left supraclavicular lymph node, the sternomanubrial junction, bilateral lung lobes, right humeral head and T7 vertebra. Further doses of RAI was planned and she is currently maintained on suppressive thyroxine therapy. Conclusion: Diagnosis of FV-PTC may be a greater challenge than conventional forms because of possible false-negative results on cytology. The infiltrative subtype has greater metastatic potential and higher recurrence rates. Multidisciplinary team management and careful preparation prior to treatment with RAI is indicated in these cases. Presentation Date: Saturday, June 17, 2023