LAUSR

BACKGROUND SMARCB1/INI1-deficient pancreatic undifferentiated rhabdoid carcinoma is a very aggressive tumor that is rarely reported in the literature. The tumor has a predominant rhabdoid cell component and different patterns of growth have been reported. CASE SUMMARY A 59-year-old woman presented with diffuse abdominal pain, increasing in severity and accompanied by weight loss, nausea, and vomiting. Imaging showed a pancreatic head mass. Fine needle aspiration demonstrated atypical epithelioid cells with a pseudopapillary growth pattern suggestive of solid pseudopapillary neoplasm. The excised neoplasm showed monotonous epithelioid and focally spindle cells with pseudopapillary structures, rhabdoid features, and loss of SMARCB1 protein expression with wild-type KRAS, consistent with a SMARCB1/INI1-deficient undifferentiated rhabdoid carcinoma. The patient’s condition deteriorated rapidly following surgery and she expired 3 mo post operation. CONCLUSION In this article, we report the first case of SMARCB1/INI1-deficient undifferentiated pancreatic rhabdoid carcinoma mimicking solid pseudopapillary neoplasm.