Prominent Papillary Growth Pattern and Severe Nuclear Pleomorphism Induced by Neoadjuvant Chemotherapy in Ovarian Mucinous Carcinoma: Potential for Misdiagnosis as High-grade Serous Carcinoma

Background/aim Histological changes induced by neoadjuvant chemotherapy (NAC) have rarely been reported in histological subtypes other than ovarian high-grade serous carcinoma (HGSC). Case report We report a 49-year-old woman whose tumors in interval debulking surgery (IDS) specimen exhibited prominent papillary growth pattern and severe nuclear pleomorphism due to NAC. In the initial microscopic examination, ovarian HGSC was the most likely candidate; however, immunostaining results were not compatible with HGSC. We detected areas resembling mucinous cystadenoma and borderline tumor, and finally diagnosed this case as ovarian mucinous carcinoma. Conclusion Although the tumor mimicked histologically HGSC, its clinical features differed from those of advanced-stage HGSC. It is important for pathologists to recognize NAC-induced histological changes, be aware of the diagnostic mimics and pitfalls, and to identify the correct histological subtype by considering the patient's previous history, clinical features, preoperative imaging findings, and histological features.