High-grade corded and hyalinized endometrioid carcinoma with high microsatellite instability and STK11 mutation: A case report and literature review.

Corded and hyalinized endometrioid carcinoma (CHEC) is a rare morphological variant of EC, characterized by biphasic histological characteristics. CHEC are predominantly low-grade, while high-grade CHEC is exceedingly rare in clinical practice. The present study reports a case of CHEC with a high-grade component in a 38-year-old female patient. Morphologically, well-differentiated EC was observed alongside corded components in the hyalinized degenerated mesenchymal tissue in the low-grade region. In the high-grade region, poorly differentiated epithelial cells, faintly visible hyalinized stroma and high nuclear grade spindle-shaped cells were observed. Immunohistochemistry demonstrated the diffuse nuclear expression of β-catenin in tumor cells. Next-generation sequencing revealed β-catenin and PIK3CA (Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha) gene mutations in both the low- and high-grade regions. Notably, the high-frequency type of microsatellite instability and mutations in serine/threonine kinase 11 were detected exclusively in the high-grade CHEC. The present study reports a case of high-grade CHEC, and simultaneously performed a review of the literature, identifying seven similar cases. Due to the rarity of such cases and the limited knowledge regarding their pathological features, there is a high risk of misdiagnosis. Further accumulation of cases is necessary to characterize CHEC.