A patient with a mucinous borderline ovarian tumor after fertility‐sparing surgery in whom puncture fluid cytology on oocyte retrieval led to a diagnosis of recurrence.

The patient was an unmarried nulliparous 21‐year‐old female who was referred to our hospital with an abdominal mass. Bilateral ovarian tumors with a solid component were detected and both were suspected to be ovarian cancer. Since the patient strongly wished to preserve fertility, we performed left salpingo‐oophorectomy, right cystectomy, and omentectomy. A postoperative histopathological examination revealed that the bilateral ovarian tumors were mucinous borderline tumors. The patient selected oocyte cryopreservation. Oocyte retrieval from the right ovary was performed 2 years after surgery, and six oocytes were obtained. The puncture of a small cyst revealed mucinous fluid, not normal follicular fluid; therefore, puncture fluid cytology was performed. A recurrent mucinous borderline ovarian tumor was suspected. Right salpingo‐oophorectomy was performed and a recurrent mucinous borderline ovarian tumor was diagnosed. Puncture fluid properties need to be considered when there is an opportunity for oocyte retrieval after fertility‐sparing surgery. [ABSTRACT FROM AUTHOR]