(P 308) IMPACT OF PSOAS MUSCLE RESECTION ON OUTCOMES IN PRIMARY RETROPERITONEAL DEDIFFERENTIATED LIPOSARCOMA

Objective: Concomitant resection of the tumor with adjacent organs and structures decreases the risk of local recurrence, the predominant issue in retroperitoneal liposarcoma. Based on a recent translational study which demonstrated a direct crosstalk between liposarcoma cells and muscle tissue, we sought to study the specific impact of ipsilateral psoas muscle resection on clinical outcomes.

Methods: Data were reviewed for all patients with primary dedifferentiated retroperitoneal liposarcoma who underwent curative intent, complete resection at a high-volume referral center from 2002 to 2023. The type of concomitant organ/structure(s) resected in each case was scrutinized. Patients with intraabdominal or pelvic tumors were excluded. Overall survival (OS) was calculated and crude cumulative incidences of local recurrence (LR) and distant metastasis (DM) were estimated. Multivariable analyses (MVA) were performed to assess the association between specific clinicopathologic factors of interest with OS, LR and DM.

Results: In this study, 437 patients were stratified into 373 who had psoas muscle resection (Ps-Y) versus 48 who did not (Ps-N). A separate cohort of 16 patients with resection of a different muscle (diaphragm or parietal, e.g., abdominal wall, D/Par) was used as a comparator to further assess psoas-specificity. OS was highest (p < 0.001) and incidence of LR was lowest (p = 0.005) in the Ps-Y compared to Ps-N and D/Par cohorts. On MVA, psoas resection had a strong association with better OS (p = 0.001) and lower LR incidence (p = 0.047), whereas there was no association with greater number of (any) organs resected (p = 0.088, p = 0.847). A trend for higher incidence of DM was observed in the D/Par versus Ps-Y and Ps-N cohorts (p = 0.115); however, on MVA, there was no association between cohorts and DM (p = 0.193). FNCLCC grade 3 disease had the strongest association with DM (p = 0.007).

Conclusion: Psoas muscle resection specifically contributes to improved local control and overall survival. This clinical study provides intriguing proof-of-concept in support of recent translational work that warrants continued investigation. In addition to amelioration of a critical soft tissue margin around the tumor, we speculate that psoas resection may potentially have direct positive impact on the disease biology.