Cellularity in myxoid liposarcoma: association with tumor immune microenvironment and patient outcomes

Background The identification of high-risk patients with myxoid liposarcoma (MLPS) remains challenging. This study aimed to describe the morphological characteristics of cellularity in MLPS and to characterize the spatial distribution and density of the tumor immune microenvironment (TIME) in MLPS. Patients and methods The morphology of untreated primary MLPS was scored for the percentage of classic, round cell, and transitional tumor components (categorized as type A, B, and C density according to a progressively higher neoplastic cellularity). TIME was evaluated by sampling the area showing the highest immune infiltrate (HI), the highest and lowest neoplastic cellularity, and the tumor border (TB). Results More than one tumor component was present in all patients ( N = 35). Most tumors harbored a classic (32/35; 91.4%) or a transitional component (34/35; 97.1%), with type C density present in 16 of 35 cases (45.7%). A round cell component was detected in 11 cases (11/35, 31.4%). In six patients who developed disease relapse, MLPS was more likely to have either a transitional component type C density, a round cell component, or both ( P = 0.014). TIME analysis showed that HI and TB on healthy tissue areas had the highest enrichment of immune cells, which were more frequently detected in transitional tumor component type C density and round cell component. Conclusions Patients with MLPS featuring a tumor with the round cell component in conjunction with transitional component type C density were at higher risk of disease progression and showed higher infiltrating T cells and tumor-associated macrophages.