Poorly differentiated chordoma: review of 53 cases.

Poorly differentiated chordoma (PDC) is a newly described variant of chordomas, which is not considered as a subtype yet, but has its own distinct features in terms of morphology, immunohistochemical and molecular characteristics, and clinical outcome. To provide a brief review of clinical, morphological, immunohistochemical, and molecular features of poorly differentiated chordoma. PubMed search using keyword 'poorly differentiated chordoma'. A critical review of all studies with a total of 53 cases using inclusion criteria of involvement of axial skeleton (vertebra and clivus), INI1 loss (either with the aid of immunohistochemistry or various molecular techniques), and immunohistochemical brachyury expression. PDC is characterized by a young population with slight female predominance, clivus/cervix location, multinodular sheets of epithelioid cells with eosinophilic cytoplasm and prominent pleomorphism, and loss of SMARCB1/INI1 expression, which can be demonstrated both with immunohistochemical and molecular studies, and is unexpected for other types of chordoma. However, classical chordomas lacking SMARCB1/INI1 expression were also reported and how to classify these cases has not been addressed yet. This unique entity is a candidate to be recognized and distinguished from other types of chordoma or SMARCB1-deficient tumors which are clinically important differential diagnoses that represent a challenging task for the pathologists.