Pathological and MRI-Based Infiltrative Markers Show Distinct Associations with Oncologic Outcomes in Undifferentiated Pleomorphic Sarcoma and Myxofibrosarcoma

Undifferentiated pleomorphic sarcoma (UPS) and myxofibrosarcoma (MFS) frequently exhibit infiltrative growth, but whether pathological and magnetic resonance imaging (MRI)-based findings represent the same tumor characteristics remain unclear. We examined the relationships among report-documented pathological infiltration (PI), MRI-defined diffuse infiltration (DI), and radiological infiltration (RI) based on the tail sign, and explored their associations with oncologic outcomes. This single-center retrospective cohort study included 68 treatment-naïve patients with primary UPS or MFS without distant or lymph-node metastasis at presentation who underwent curative-intent resection. The primary outcome was progression-free survival (PFS), with overall survival (OS), distant metastasis-free survival (DMFS), and local recurrence-free survival (LRFS) evaluated as secondary outcomes. Time-to-event associations were evaluated using Firth’s penalized Cox regression with parsimonious covariate adjustment and sensitivity analyses restricted to patients with R0 resection. DI, RI, and PI were observed in 75.0%, 76.5%, and 60.3% of patients, respectively. RI positivity was more frequent among patients with PI, whereas DI showed no clear relationship with PI or RI. In an exploratory multivariable model, DI (hazard ratio [HR], 3.30; 95% confidence interval [CI], 1.05–16.51; p = 0.040) and RI (HR, 4.26; 95% CI, 1.31–22.29; p = 0.013) were associated with worse PFS. Local recurrences occurred only in patients with PI, although adjusted estimates were imprecise. These findings suggest that pathological and MRI-based infiltrative markers may capture different and potentially complementary aspects of tumor behavior. External validation using standardized imaging and pathological review is required.