Papillary thyroid cancer with extrathyroidal extension of desmoid-type fibromatosis. A case report of an aggressive presentation of an uncommon pathologic entity

INTRODUCTION: Papillary thyroid cancer with desmoid-type fibromatosis (PTC-DTF) is an uncommon tumor characterized by extensive stromal proliferation of fibroblasts and myofibroblasts with a small component of PTC. We report a case of PTC-DTF with infiltration of the mesenchymal component of tumor into perithyroidal muscle and early recurrence of desmoid after thyroidectomy, an outcome previously not reported. PRESENTATION OF CASE: A 20-year-old man underwent left hemithyroidectomy for a thyroid nodule. Pathology demonstrated a 4.2 cm tumor with PTC-DTF with the PTC comprising <10% of the tumor. The stromal component extended into adjacent skeletal muscle. After completion thyroidectomy, histopathology of the right thyroid lobe revealed no malignancy or fibromatosis. Neck MRI 16 months after the initial operation revealed a 10.5 cm tumor in the left thyroid bed. Core biopsy and open excisional biopsy showed desmoid-type fibromatosis without PTC. The patient is undergoing chemotherapy of his recurrent desmoid-type fibromatosis. DISCUSSION: In patients with PTC-DTF there is a risk of recurrence of the benign component of the tumor. In recent reports, the role of less aggressive surgery, or even non-surgical management, of patients with recurrent DTF has been emphasized, in particular when extensive surgery may be associated with high risk of functional loss. The management of our patient adheres to modern recommendations for the treatment of DTF. CONCLUSION: Patients with PTC-DTF should be carefully monitored after thyroidectomy for both recurrent PTC and local recurrence of the fibrous component of the tumor.