[Clinicopathological features of notochordal tumors: a study of 48 cases]

Objective: To investigate the clinicopathological features, diagnosis and differential diagnosis of notochordal tumors. Methods: The clinical, radiologic and pathologic data of 48 notochordal tumors were collected from 2008 to 2019 at Shanghai Jiaotong University Sixth People's Hospital. Expression of cytokertin, S-100 protein, vimentin, brachyury and INI1 was detected by immunohistochemistry. The pathologic differential diagnoses and biologic behavior of various types of notochordal tumors were analyzed using the new standard in the 5th edition of WHO tumor classification. Results: Four cases of benign notochordal cell tumor were confined to vertebral body. Histopathologically, they lacked lobular architecture and extracellular myxoid matrix. The tumor cells were vacuolated and had centrally or peripherally located round to oval nuclei, with small nucleoli, without atypia, mimicking mature adipocytes. No mitotic figures were seen. Two cases of poorly differentiated chordoma, from patients aged 12 years and 21 years respectively, were located in cervical vertebra, and were composed of cohesive sheets or nests of epithelioid cells, with focal rhabdoid morphology. There was relatively abundant eosinophilic cytoplasm and scattered cytoplasmic vacuoles. The moderately pleomorphic nuclei were round to ovoid with vesicular chromatin and mitotic figures could be seen. Extracellular myxoid stroma was observed focally. Forty cases of conventional chordoma and two cases of extra-axis chordoma had similar histologic features. All 48 cases expressed cytokeretin, 45 cases expressed brachyury, and two poorly differentiated tumors showed loss of INI1/SMARCB1. Conclusions: There are four subtypes of chordomas: conventional, dedifferentiated, poorly differentiated and extra-axis. Chondroid chordoma is no longer thought to be a distinct entity. Each type has its unique clinicopathological characteristics. Brachyury is highly specific and sensitive for the diagnosis of various notochordal tumors. Poorly differentiated chordoma shows distinct clinicopathological features, including young age and loss of immunohistochemical expression of INI1/SMARCB1, and its diagnosis requires the combined detection of brachyury and INI1/SMARCB1.