This was an exceptionally large mass (10.1 cm in length) compared to human pancreatic UPS/MFHs, whose largest recorded dimension is 35 cm.9 In the light of the high Ki‐67 labeling index, obtained immunohistochemically, the surprisingly large tumor found in our young adult rat provides evidence of the aggressive nature of the malignancy. Here, MKI67 is linked to neoplasm.