A Case Illustrating Challenges: Early-Onset Signet Ring Cell Rectal Carcinoma With Fulminant Peritoneal Progression.

Signet ring cell carcinoma (SRCC) of the rectum is a rare histologic subtype and is often associated with aggressive behavior and poor outcomes, particularly in young patients. We report a 19-year-old male who presented with acute intestinal obstruction and was diagnosed with rectal SRCC, radiologically staged as cT2N1bM0, acknowledging the limitations of radiologic staging in this histologic subtype. An emergency diversion colostomy was performed, followed by long-course neoadjuvant chemoradiotherapy (nCRT). Three months later, the patient presented again with abdominal pain and cachexia. Radiology showed evidence of extensive peritoneal disease. Exploratory surgery revealed diffuse peritoneal carcinomatosis, preventing the planned complete cytoreduction and hyperthermic intraperitoneal chemotherapy. Further treatment options were discarded by the family. The disease progressed rapidly, and the patient passed away one month later. This case highlights the challenges in early-onset rectal SRCC. The aggressive clinical course even after long-course neoadjuvant chemoradiotherapy, the limitations of current treatment protocols, and the high risk of understaging through conventional radiology are highlighted in this case report.