Pathological features and clinicopathological significance of TERT promoter mutation in breast fibroepithelial tumors without definite diagnosis

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Objective: To investigate the pathological features and the clinicopathological significance of TERT detection in those tumors that were difficult to diagnosis. Methods: A total of 93 cases of fibroepithelial tumors without definite diagnosis were collected from the Affiliated Hospital of Qigndao University between 2013 and 2021. The clinical details such as patients' age and tumor size were collected. All slides were re-reviewed and the pathologic parameters, including stromal cellularity, stromal cell atypia, stromal cell mitoses, and stromal overgrowth were re-interpreted. Sanger sequencing was used to detect TERT promoter status, and immunohistochemistry was performed to detect TERT protein expression. The relationship between TERT promoter mutation as well as protein expression levels and the clinicopathological parameters were also analyzed. Results: The patients' ages ranged from 30 to 71 years (mean of 46 years); the tumor size ranged from 1.2 to 8.0 cm (mean 3.8 cm). These tumors showed the following morphologic features: leafy structures in the background of fibroadenoma, or moderately to severely abundant stromal cells. The interpretations of tumor border status were ambiguous in some cases. The incidence of TERT promoter mutation was high in patients of age≥50 years, tumor size≥4 cm, and stromal overgrowth at ×4 or ×10 objective, and these clinicopathologic features were in favor of diagnosis of phyllodes tumors. TERT protein expression levels was not associated with the above clinicopathologic parameters and its promoter mutation status. Conclusions: The diagnostic difficulty for the breast fibroepithelial tumors is due to the difficulty in recognition of the leafy structures or in those cases with abundant stromal cells. A comprehensive evaluation combined with morphologic characteristics and molecular parameters such as TERT promoter may be helpful for the correct diagnosis and better evaluating recurrence risk.