(P 242) WHOLE BODY PET/MRI FOR STAGING OF MYXOID LIPOSARCOMA

Objective: Myxoid liposarcoma (MLS) has a unique predilection for metastasis to rare sites. The National Comprehensive Cancer Network (NCCN) recommends staging with computed tomography (CT) of the chest, abdomen, and pelvis and magnetic resonance imaging (MRI) of the entire spine. This study compares the performance of whole body scanning using positron emission tomography (PET) plus MRI and/or CT with NCCN guidelines.

Methods: A retrospective case series was conducted including patients with biopsy proven MLS from2015 to 2022. Patients were excluded if they 1) did not complete staging, or 2) had their care outside our institution. Patients were separated into cohorts based upon whether they were staged initially with whole body PET/MRI, or standard NCCN staging regimen of CT chest/abdomen/pelvis and whole spine MRI. We recorded detection of initial metastases, standardized uptake value (SUV) of primary tumor and metastatic lesions, and development of local recurrence and/or new metastases. Kruskal-Wallis and Fisher’s exact test were used to compare continuous and categorical variables, respectively.

Results: In total 31 patients with MLS were identified who had complete staging. 21 of these had staging completed with whole body PET/MRI or PET/CT, and the other 10 had staging with standard NCCN approach. Three (14.3%) patients in the PET group had metastatic disease on initial presentation and no initial metastases were identified in the NCCN group (Table 1). The three patients with initial metastatic disease had a total of 6 metastatic locations, all of which would have been detected by NCCN guidelines. Two patients in the initial NCCN group had new metastases discovered by CT chest or MRI spine. Three patients in the initial PET group had new metastases discovered by whole body PET/MRI or MRI spine. As shown in Table 1, the SUV of primary and metastatic lesions was 3.6 and 3.2, respectively.

Conclusion: Our data indicate that whole-body PET modalities for staging MLS appears to detect initial and new metastatic disease as well as current NCCN guidelines. The added value of the PET is questionable given the very low SUV of primary and metastatic lesions. Whole body staging, with or without PET, offers the advantages of a simplified and expedited staging regimen. Given that the numbers in this study are low, it is important to study this topic further either in a collaborative study design.