73P Tumor localisation and oncological outcomes in non-uterine leiomyosarcoma of the abdomen and pelvis

Leiomyosarcoma (LMS) is the second largest group of soft tissue sarcomas and often has an aggressive tumor biology. While evidence supports different biological behavior between uterine (ULMS) and non-uterine leiomyosarcomas (NULMS), the data on clinical outcome for NULMS depending on tumor localization (ie. visceral, retroperitoneal and pelvic) is scarce. This study aimed to analyze the association between tumor localization and oncological outcomes in NULMS. Pts with LMS located in the abdomen and pelvis diagnosed between 2005 and 2022 were identified in the institutional sarcoma database at the Norwegian Radium Hospital. Non-operated, ULMS or pts with missing data were excluded. Included pts were divided into 3 subgroups based on primary tumor localisation: visceral, retroperitoneal and pelvic. A total of 123 pts (73 women) with a median age 62 years were included in the study. There were 48 pts in the retroperitoneal, 35 pts in the visceral and 40 pts in the pelvic subgroup. Median tumor size was 8 (1-32) cm. Retroperitoneal tumors were significantly larger than visceral, median 10.0 cm vs. 5.5 cm; P=0.048. 52 pts had French malignancy grade III. No significant differences in malignancy grade between the subgroups were observed. A free microscopic margin (R0) was achieved in 79 (66%) pts. The R0 rate was lower in the retroperitoneal and pelvic subgroups than for visceral tumors, 46% and 71% vs. 82% respectively; P=0.048. The median follow-up time was 23 (1-135) months. Fifty (47%) pts had disease recurrence; 16 (32%) local recurrences and 34 (68%) pts distant metastases. The median time to recurrence was 8 (3-54) months. The entire cohort's 5- and 10-year OS was 70% and 34%. For pts with retroperitoneal tumors, 5- and 10-year OS was 52% and 24% vs. 61% and 41% in the pelvic and 70% vs. 63% in the visceral subgroup; P=0.018. 5- and 10-year DFS was 30% and 10% for patients with retroperitoneal tumors, 49% and 32% for patients with pelvic tumors and 46% and 36% in the visceral subgroup; P=0.167. The median time from relapse to death was 21 (1-88) months. Pts with visceral LMS had better oncological outcomes compared to pts with retroperitoneal tumors. Recurrence rates were high and long-term outcome after disease relapse was dismal.