Clinicopathologic features of SMARCB1/INI1-deficient pancreatic undifferentiated rhabdoid carcinoma: A case report and review of literature

BACKGROUND SMARCB1/INI1-deficient pancreatic undifferentiated rhabdoid carcinoma is a highly aggressive tumor, and spontaneous splenic rupture (SSR) as its presenting manifestation is rarely reported among pancreatic malignancies. CASE SUMMARY We herein report a rare case of a 59-year-old female who presented with acute left upper quadrant abdominal pain without any history of trauma. Abdominal imaging demonstrated a heterogeneous splenic lesion with hemoperitoneum, raising clinical suspicion of SSR. Emergency laparotomy revealed a pancreatic tumor invading the spleen and left kidney, with associated splenic rupture and dense adhesions, necessitating en bloc resection of the distal pancreas, spleen, and left kidney. Histopathology revealed a biphasic malignancy composed of moderately differentiated pancreatic ductal adenocarcinoma and an undifferentiated carcinoma with rhabdoid morphology and loss of SMARCB1 expression. Immunohistochemical analysis confirmed complete loss of SMARCB1/INI1 in the undifferentiated component, along with a high Ki-67 index (approximately 80%) and CD10 positivity. The ductal adenocarcinoma component retained SMARCB1/INI1 expression and was positive for CK7 and CK-pan. Transitional zones between the two tumor components suggested progressive dedifferentiation and underlying genomic instability. The patient received adjuvant chemotherapy with gemcitabine and nab-paclitaxel and maintained a satisfactory quality of life at the 6-month follow-up. CONCLUSION This study reports a rare case of SMARCB1/INI1-deficient undifferentiated rhabdoid carcinoma of the pancreas combined with ductal adenocarcinoma, presenting as SSR - an exceptionally uncommon initial manifestation of pancreatic malignancy.