Poorly Differentiated Chordomas Showing Loss of INI1/SMARCB1: A Report of 2 Rare Cases With Diagnostic Implications.

Poorly differentiated chordomas are rare musculoskeletal tumors. Case 1. A 42-year-old lady presented with quadriparesis of 2 months' duration. Radiologic imaging disclosed a soft tissue mass in her left prevertebral- and paravertebral cervical region. Case 2. A 4-year-old male child presented with neck pain and restricted head movements of 1-year duration. Radiologic imaging revealed a contrast enhancing, paraspinal soft tissue mass in his cervical region. Microscopic examination in both the cases revealed a cellular malignant tumor composed of moderate to markedly pleomorphic cells with interspersed mitotic figures, along with focal myxoid change and necrosis. By immunohistochemistry, tumor cells in both cases were diffusely positive for pan cytokeratin (AE1/AE3) and brachyury, whereas these were negative for INI1/SMARCB1. Tumor cells in the second case were also positive for glypican3. The first case developed pulmonary metastasis, while the second case developed recurrence. Poorly differentiated chordomas are uncommon tumors, invariably characterized by loss of INI1. These tumors can be rarely seen in adults and need to be differentiated from their diagnostic mimics, in view of treatment implications and their relatively aggressive clinical outcomes.