Detection of TROP2: Ushering in a new choice in the treatment of patients with special types of invasive breast cancer.

1106 Background: TROP2 has become an attractive new therapeutic target in breast cancer (BC). TROPiCS-02 trial shows that the sacituzumab govitecan(SG) which is the TROP2 ADC drug can significantly benefit the survival of patients with TNBC and HR+/HER2- BC, and the 2023 ASCO guideline recommends that TROP2 detection is not necessary before the SG treatment. However, less than 5% BC patients of special subtype were included in clinical trials, and the TROP2 expression of them is not yet known. The aim of our study is to compare the expression of TROP2 in different special types of BC, and provide reference for targeted treatment of these patients. Methods: We retrospectively retrieved tissues from 383 patients diagnosed with special type of BC and undergoing surgical resection at our institution from 2018 to 2023. Including metaplastic carcinoma (MBC), mucinous carcinoma (MC), adenoid cystic carcinoma, cribriform carcinoma, carcinoma with apocrine differentiation, neuroendocrine carcinoma and tubular carcinoma. Classify them as TNBC or HR+/HER2- BC. Applying H-score to evaluate the TROP2 expression, H-score<100, 100~200, and 201~300 classified as low, moderate and high expression. Results: Expression of TROP2 is higher in tubular and cribriform carcinoma, while in MBC and MC is significantly lower (χ 2 =66.756, P<0.001) (Table). Low expression of TROP2 is associated with low clinical staging ( P<0.05), no lymph node metastasis ( P<0.05), and high-grade tumor infiltrating lymphocytes ( P<0.05). Moreover, TROP2 had the lowest expression in MBC, with a median H-score of 45. There are 78.13% (43/55) cases showed H-score<100, with 27.3% (15/55) of cases showing no expression of TROP2 at all. It is worth noting that MBC is highly invasive and has a poor prognosis, but the expression level of TROP2 is very low in mesenchymal cells, while in squamous differentiated tumor tissue, the expression level of TROP2 is high, and the overall H-Score score is low ( P<0.001). Conclusions: This study is the first preliminary study on the TROP2 expression in special types of breast cancer. Although the current ASCO guideline recommends not testing TROP2, but our study shows it is pretty low or even not expressed in MBC and MC. Notably, the lack of expression in the mesenchymal and spindle cell subtypes may be highly indicates that they lack epithelial tumor cells expressing TROP2 as vectors, resulting in the inability to exert the therapeutic effect of ADC, we suggest routine testing of TROP2. Table: see text