Poorly Differentiated Chordoma

**Semantic type:** Neoplastic Process

**Definition:** A rare, aggressive type of chordoma characterized by loss of SMARCB1 expression. It affects children and occasionally young adults. Females are affected twice as frequently as males. It usually arises in the axial skeleton. It is composed of sheets or nests of malignant epithelioid cells with abundant eosinophilic cytoplasm. The prognosis is poor.