Preoperative diagnosis in gynecologic oncology often remains a significant challenge for the medical team, even today, when imaging techniques have reached an advanced stage of development. These difficulties are particularly evident in rare tumors and in locally advanced disease, where establishing the tumor’s origin is complex. Multidisciplinary collaboration in such cases is essential for improving prognosis and optimizing therapeutic management. We present a series of three clinical cases in which the initial diagnosis was redefined after histopathological examination: two cases of ovarian neoplasm, one of which was ultimately identified as an ovarian neuroendocrine tumor – an extremely rare entity worldwide – and one case initially suspected clinically and radiologically as endometrial sarcoma, but postoperatively confirmed as a large benign endometrial polyp. We highlight the usefulness of performing cell block preparations from ascitic or pleural fluid rather than open biopsy in ovarian neoplasms, thereby reducing perioperative risks. This article emphasizes the importance of integrating clinical and paraclinical findings to minimize diagnostic errors, particularly in atypical presentations.