INI1-Deficient malignancy involving the pancreas and jejunum: Expanding the clinical spectrum

<i>SMARCB1</i>/integrase interactor 1(INI1)-deficient malignancies of the gastrointestinal (GI) tract are exceedingly rare, poorly characterized, and notoriously aggressive, posing substantial diagnostic challenges for radiologists due to their nonspecific imaging features and overlap with more common neoplasms. Additionally, fewer than 50 cases of INI1-deficient GI carcinomas have been documented, making their recognition on imaging alone exceptionally challenging. We present a case of a 25-year-old female with a rapidly enlarging INI1-deficient poorly differentiated tumor involving both the pancreas and jejunum which is an unreported combination. It demonstrated explosive growth on short-interval computed tomography (CT) and early widespread metastases despite extensive surgical resection. This case highlights the critical role of radiologists in early recognition and management of such rare entities by identifying disproportionate interval growth, recommending repeat staging or Positron Emission Tomography-Computed Tomography (PET-CT) prior to surgery, and expediting histopathologic and immunohistochemical correlation. Given their rapid progression, poor response to conventional therapies, and dismal prognosis, heightened awareness and radiologic vigilance are essential for guiding management and avoiding delays in diagnosis for these exceptionally uncommon but lethal neoplasms.