S4003 Unmasking the Rarity: A Case of Primary Signet-Ring Cell Carcinoma of the Colon in a Young Female

Introduction: Primary signet-ring-cell carcinoma of the colon and rectum (PSRCCR) is a rare and aggressive subtype of colorectal cancer, accounting for 0.1%–1% of cases. It is associated with poor prognosis, advanced disease at diagnosis, high rates of peritoneal metastasis, and lower survival rates compared to other colorectal cancers. First identified in 1951, PSRCCR is classified as a variant of mucinous adenocarcinoma, typically presenting as diffuse, circumferential bowel wall thickening that can mimic inflammatory bowel disease, leading to delayed diagnosis. Its aggressive nature often results in high rates of lymphovascular invasion and peritoneal dissemination, occurring in over 50% of cases. Although most cases occur in older adults, primary cases in younger individuals are exceptionally rare. Here, we report an unusual case of PSRCCR in a 29-year-old woman. Case Description/Methods: A 29-year-old woman with a medical history of organ transplantation, hypertension, type 2 diabetes, and recent cholecystectomy presented with severe abdominal pain, obstipation, and vomiting. Computed tomography revealed a small bowel obstruction and an 8 cm cecal mass involving the ileocecal valve, with pericecal soft tissue infiltration and lymphadenopathy. Differential diagnoses included a primary colonic neoplasm or lymphoproliferative neoplasia. The patient underwent exploratory laparotomy for mass resection and right hemicolectomy. Biopsies indicated poorly differentiated grade 3 signet-ring cell carcinoma with mucinous features, classified as pT4a pN2b cM1c due to peritoneal metastasis. There was no loss of mismatch repair proteins, and the probability of microsatellite instability was low. Positron emission tomography scan suggested possible peritoneal carcinomatosis, and chemotherapy was initiated. Discussion: PSRCCR is particularly uncommon in younger populations, with limited case reports highlighting the challenges in diagnosis and management. The rarity in individuals under 30 is likely due to the typical age distribution of colorectal cancer, which predominantly affects older adults. The distinct histological features of PSRCCR contribute to delayed diagnosis, as symptoms may mimic other gastrointestinal conditions. Increased awareness among clinicians is essential for timely identification of PSRCCR in younger patients presenting with gastrointestinal symptoms. This case underscores the need for prompt evaluation and appropriate diagnostic imaging to facilitate early diagnosis and intervention, ultimately improving outcomes for affected individuals.