Title Rapid growth of mitotically active cellular fibroma of the ovary : a casereport and review of the literature

Background: Mitotically active cellular fibroma (MACF) of the ovary, characterized by relatively high mitotic activity without severe atypia, represents a relatively new disease entity. MACF is categorized as a benign ovarian tumor. However, due to a limited number of case reports, its clinical and pathological features and optimum management remains largely undetermined. Herein, we report on a rare case of MACF that grew rapidly in size and was diagnosed on detailed pathological examination. Case presentation: A 44-year-old Japanese woman, who detected a myoma-like lesion 1-year earlier, was referred to our hospital when the follow-up examination demonstrated that the mass had increased in size. Magnetic resonance imaging revealed a T1 isointense and T2 hyperintense tumor (11 cm in diameter) in the right pelvic cavity. Laparoscopy confirmed the presence of a right ovarian tumor and laparoscopic right adnexectomy was performed. The tumor cells consisted of dense cellular proliferations of spindle fibroblast-like cells without significant cytological atypia. The mitotic activity index was estimated at >15 mitotic figures per 10 high-power fields. Reticulin staining and FOXL2 mutation analysis excluded the possibility of an adult granulosa cell tumor, and the patient was diagnosed with a MACF of the ovary. Conclusions: To the best of our knowledge, we are the first to report on a case of rapid growth of a MACF of the ovary during follow-up. When an increase in the size of a solid ovarian mass is detected, a MACF should be considered as a differential diagnosis.