To determine the incidence of occult uterine sarcomas and other unexpected pathologies in patients undergoing hysterectomies or myomectomies with a pre-operative diagnosis of uterine leiomyomas.

Retrospective study.

Tertiary hospital in Santiago, Chile.

921 women who underwent surgery for presumed myomas.

Database analysis of surgical and pathological notes, from January 2007 to December 2017 with a preoperative diagnosis of uterine leiomyoma.

number of patients with uterine sarcoma confirmed on histology.

During this period, a total of 921 gynecological surgeries were performed for benign uterine fibroids of which 787 were hysterectomies and 134 were myomectomies. We found four cases of malignant neoplasms (0,43 %). Two were uterine leiomyosarcoma (LMS), one mixed epithelial and mesenchymal tumor, and one case of incidental cervical cancer. This gives an LMS incidence of 1 in 460 and 1 in 921 of mixed epithelial and mesenchymal tumor. There were seven cases of unexpected benign pathology. This included six atypical myomas and one leiomyoblastoma epithelioid myoma. If we combine the malignant and benign cases, we would have an incidence of 1.2 % of unexpected pathology.

In our series of patients undergoing myomectomies or hysterectomies for presumed myomas the incidence of LMS was 1 in 460. The incidence of any unexpected pathology including benign ones in presumed myomas was 1 in 83 (six atypical myomas, one leiomyoblastoma epithelioid myoma, two LMS, one mixed epithelial and mesenchymal tumor, one incidental cervical cancer).