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

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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.