Papillary thyroid carcinoma with desmoid-type fibromatosis: the clinicopathological features with characteristic imaging and molecular correlation requiring comprehensive treatment

The pathogenesis and treatment of papillary thyroid cancer with desmoid-type fibromatosis (PTC-DTF), a rare subtype of papillary thyroid carcinoma characterized by a mixed epithelial-mesenchymal structure, are still ill-defined. Previous reports on PTC-DTF have had limited follow-up and recurrence has been rarely reported. To better understand this condition, we conducted a thorough analysis of five cases of PTC-DTF from our institute, including clinical and pathological examinations, imaging, immunohistochemistry, and molecular analysis. We also reviewed relevant literature. The mean age of the patients was 51.8 years, with three women and two men included in the group. Ultrasound often showed a hypoechogenic and well-defined nodule in the thyroid gland, except for one individual who had distant lung metastases detected by PET-CT. The nodules ranged in width from 0.5 to 5.0 cm and were excised in each case. Following surgery, 131I therapy was used in two cases. The overall number of PTC-DTF cases has risen from the previously reported 55 to 60, with females being the most commonly affected and ranging in age from 19 to 82. Most masses underwent a thyroidectomy, and approximately half of the patients had lymph node metastases. Histologically, PTC-DTFs were composed of a predominant stromal component (65%-90%) and an intervening epithelial component. These spindle cells were arranged in parallel with abundant cytoplasm and vacuole-like nucleus but there wasn't evident atypia. The carcinoma cells were positively stained for CK and TTF-1 by immunohistochemistry, whereas mesenchymal cells were positive for SMA and displayed nuclear immunoreactivity for β-catenin. BRAF, NRAS, and CTNNB1 mutations were identified in the epithelial and mesenchymal components through molecular testing, respectively. Perhaps because the mesenchyme harbors aberrant nuclear β-catenin expression, PTC-DTF is more aggressive and prone to invasion and distant recurrence, as shown by our case 2, which is the first case to be reported thus far. PTC-DTF is typically treated with surgery, but clinicians may occasionally consider more holistic treatment plans that involve radioactive iodine and endocrine therapy.