Clinicopathologic Characteristics and Prognostic Value of Rhabdoid Features in Pancreatic Undifferentiated Carcinoma.

Undifferentiated carcinoma (UC) is a rare, highly aggressive subtype of pancreatic cancer; UC with rhabdoid features (UCRF) is particularly associated with poor prognosis. This study aimed to compare clinicopathologic characteristics and outcomes of UC between groups of patients defined by presence versus absence of RF. We retrospectively reviewed patients diagnosed with UC by EUS-guided tissue acquisition from 2017 to 2024. Histologically, 11 patients were classified as anaplastic UC and two had UC with osteoclast-like giant cell. Six patients had UCRF. Only 2 patients underwent surgery, while 8 received chemotherapy; 5 of these were treated with gemcitabine plus nab-paclitaxel. One patient (17%) in the UCRF group was INI-1-negative. CK7 was positive in 3 UCRF patients (50%) and in all 7 UC patients without RF. In the overall cohort, median OS showed no statistically significant difference between UCRF and UC without RF (3.9 vs. 12.9 months; log-rank p = 0.188). However, after excluding two patients with UCOGC, Kaplan-Meier analysis demonstrated a significantly shorter OS in UCRF (p = 0.009). These findings suggest that RF represents a potential adverse prognostic factor in pancreatic UC. Further studies are warranted to clarify biologic significance and treatment implications of RF in pancreatic UC.