Diffuse sclerosing variant of papillary thyroid carcinoma--an update of its clinicopathological features and molecular biology.

Diffuse sclerosing variant of papillary thyroid carcinoma (DSVPTC) is an uncommon variant of papillary thyroid carcinoma. The aim of this review is to critically analyse the features of this entity. A search of the literature revealed 25 clinicopathological studies with in-depth analysis of features of DSVPTC. Overall, the prevalence of DSVPTC varies from 0.7-6.6% of all papillary thyroid carcinoma. Higher prevalence of DSVPTC was noted in paediatric patients and in patients affected by irradiation. DSVPTC tends to occur more frequently in women and in patients in the third decade of life. Macroscopically, DSVPTC can involve the thyroid gland extensively without forming a dominant mass. Microscopic examination of DSVPTC revealed extensive fibrosis, squamous metaplasia and numerous psammoma bodies. The latter pathological feature can aid in the pre-operative diagnosis of the entity by fine needle aspiration and ultrasound. Compared to conventional papillary thyroid carcinoma, DSVPTC had a higher incidence of lymph node metastases at presentation. Distant metastases were noted in approximately 5% of the cases. Patients with DSVPTC were recommended to be managed by aggressive treatment protocols. It is likely that as a result of this, the prognosis of the patients with DSVPTC was noted to be similar to conventional papillary thyroid carcinoma. Overall, cancer recurrence and cancer related mortality have been reported in 14% and 3%, respectively, of patients with DSVPTC. In immunohistochemical studies, DSVPTC showed different expression patterns of epithelial membrane antigen, galectin 3, cell adhesion molecules, p53 and p63 when compared to conventional papillary thyroid carcinoma. On genetic analysis, the occurrence of BRAF and RAS mutations are uncommon events in DSVPTC and activation of RET/PTC rearrangements are common. To conclude, DSVPTC has different clinical, pathological and molecular profiles when compared to conventional papillary thyroid carcinoma.