HER2 Evaluation in Uterine Serous Carcinoma: Diagnostic Agreement Between Biopsy and Resection Samples

Background Uterine serous carcinoma (USC) is a very aggressive variant of endometrial cancer, contributing to a disproportionate incidence of recurrences and cancer-related mortality, albeit representing a minority of cases. HER2 overexpression and amplification have become important prognostic and predictive indicators in USC, endorsing the application of HER2-targeted treatments. Nonetheless, obstacles including intratumoral heterogeneity and inconsistencies between biopsy and resection tissues hinder precise HER2 evaluation. Methods This retrospective analysis examined 40 instances of USC diagnosed from 2010 to 2020. Expressions of HER2, ER, PR, and Ki-67 were analyzed via immunohistochemistry (IHC), whereas HER2 gene amplification was determined using chromogenic in situ hybridization (CISH). The concordance between biopsy and resection specimens was evaluated. The statistical associations between HER2 status and clinicopathological factors were analyzed utilizing t-tests and chi-square tests. Results HER2 positive demonstrated a strong link with elevated FIGO stage (p = 0.0060) and an enhanced Ki-67 proliferation index (p = 0.0002), indicating a relationship with more aggressive illness. A strong concordance was established between biopsy and resection HER2 values (PPV = 100%, NPV = 91.4%), however differences were identified in 7 instances. CISH was negative in all IHC 0 patients and positive in 3 of the 2 + cases. HER2 gene amplification was detected in one IHC 1 + instance, underscoring the clinical significance of HER2-low tumors in USC and highlighting the necessity of molecular confirmation in ambiguous cases. Conclusion The precise evaluation of HER2 in USC is essential but hindered by tumor heterogeneity and the type of sample used. Standardized HER2 testing criteria unique to USC, along with the evaluation of HER2-low tumors and retesting procedures in metastatic contexts, are crucial for enhancing therapy outcomes.