T-pit is a novel, sensitive biomarker for conventional chordoma.

T-PIT is a reliable and sensitive marker for the diagnosis of corticotroph tumors, particularly in histologically atypical cases. During routine clinical work, we incidentally observed positive T-PIT expression in chordoma. To further clarify the diagnostic utility of T-PIT, we evaluated its immunohistochemical expression alongside that of brachyury in a series of tumors, including chordoma (n = 23), corticotroph tumors (n = 29), hemangioblastoma (n = 10), chordoid meningiomas (n = 2), chordoid glioma (n = 3), low-grade chondrosarcoma (n = 4), small cell carcinoma (n = 4), germinoma (n = 5) and low-grade glioma (n = 38). Notably, all chordoma cases (100%)-comprising 18 primary and 5 recurrent tumors-exhibited concurrent positivity for both T-PIT and brachyury. All cases of corticotroph tumors expressed T-PIT protein but were negative for brachyury protein. Sixty percent of germinoma cases expressed T-PIT, and 100% expressed brachyury. However, T-PIT and brachyury were not expressed in any cases of hemangioblastomas, chordoid meningiomas, chordoid glioma, low-grade chondrosarcoma, small cell carcinoma, or low-grade glioma. Our study indicated that T-PIT expression, as well as brachyury expression, is commonly observed in chordoma. Although corticotroph adenomas (PitNET) do not resemble the histology of chordomas, using T-PIT positivity alone as a diagnostic marker for these tumors may lead to misdiagnosis.Our findings also provide new insights into the role of T-PIT in notochord development and chordoma formation.