Rottmann D, Snir OL, Wu X, et al. - Tumors from 80 patients (65 uterine, 15 tubo-ovarian) were involved, comprising a serous, endometrioid, clear cell, undifferentiated, neuroendocrine, or mixed carcinoma, and either a homologous, or a heterologous sarcoma component in order to systematically assess the features of HER2 expression/amplification in gynecologic carcinosarcomas using standardized staining methods and scoring criteria. Using the 2013 criteria, a total of 13 cases (12 uterine, one ovarian) were HER2 positive (either by immunohistochemistry or FISH) while as per the 2007 criteria, only ten cases (nine uterine, one ovarian) were HER2 positive. Between the two scoring systems, nine cases revealed an alteration in their HER2 immunohistochemical score, comprising two cases with a modification in the overall HER2 status from negative to positive. In 38% of HER2-positive tumors, the heterogeneity of HER2 protein expression was perceived as a lateral/basolateral membranous staining pattern was prevalent. The sarcoma component exhibited 2+, equivocal HER2 expression in five cases, one of which also illustrated HER2 amplification by FISH. Every HER2-positive carcinosarcoma had either a serous or a mixed carcinoma component, and all although, one HER2-positive tumor was of uterine primaries. Thus, gynecologic carcinosarcomas share similarities to endometrial serous carcinomas in their HER2 expression/amplification profiles, which should be considered when evaluating their HER2 status to ensure relevant patient selection for potential targeted HER2-based therapies in the future.