Introduction/Background Uterine leiomyosarcomas (LMS) are the most frequent uterine sarcomas and about 43% of them are diagnosed after hysterectomy performed for presumed benign disease. The incidence of unexpected LMS can reach 0.49%. The purpose of this study is to report the oncological outcomes of patients who had incidental finding of unexpected LMS following hysterectomy and compare them to those of women who had surgery for suspected LMS.

Methodology A retrospective study was conducted on 5.528 consecutive patients who underwent hysterectomy at the Filippo del Ponte hospital of Varese from 2000 to 2019. Baseline characteristics, relapse rate and pattern of recurrence were analysed by stratifying the population in suspicious/unexpected LMS. The oncologic outcomes and risk factors, including surgical approach were analysed. Risk factor for LMS were also evaluated.

Results Among 4428 suspect benign cases, 24 unexpected LMS were found (0.54%). Malignancy was preoperatively suspected in 1.100 cases and 12 LMS were found at final histology (1.09%). Baseline characteristics did not differ between the groups. In the unexpected-LMS group, 15(62.5%) patients had laparoscopic approach (LPS), 14(58.3%) had morcellation and 2/14(14.3%) was contained. In the suspect group 9(75%) of patients underwent open surgery, 3(25%) LPS were performed, 1 had in-bag morcellation. In the comparison between unexpected vs. suspicious LMS, no factors influencing prognosis were identified. Among patients who had laparoscopic approach, a higher rate of loco-regional relapse was found (LPS 78% vs. Open 33.3%, p= 0.04).

Conclusion The incidence of unexpected LMS in women undergoing hysterectomy for benign disease was 1/185 (0.54%). The preoperative malignant suspicion in patients undergoing total hysterectomy with subsequent LMS diagnosis did not affect the oncological outcomes. No predictors of relapse were identified. LPS was associate to higher rates of loco-regional relapse. Increased age, uterine weight and menopausal status were associated with higher risk of LMS.