S3962 Catastrophe From the Colon: A Case of Metastatic Colon Cancer During Pregnancy

Introduction: Cancer during pregnancy is rare, with an estimated incidence of 0.07% to 0.1% of all pregnancies. Among these, colorectal cancer (CRC) is exceedingly uncommon, occurring in approximately 1 in 13,000 pregnancies (0.008%). We present the case of a 38-year-old woman diagnosed with colon cancer during her second trimester to highlight the challenges and considerations involved in managing colon cancer while preserving fetal viability. Case Description/Methods: A 38-year-old gravida 3 para 2 woman who presented at 23 weeks and 6 days of gestation with abdominal pain. Magnetic resonance imaging of abdomen and pelvis revealed a large heterogeneous left adnexal mass with extensive peritoneal involvement, initially raising concern for a primary ovarian malignancy. Tumor markers including CEA, CA 19-9, and AFP were elevated, and biopsy of the peritoneal implants revealed metastatic well-differentiated mucinous adenocarcinoma. Immunohistochemical staining was positive for CDX2, CK20, and p16, and negative for PAX8, CK7, and other Müllerian markers, confirming a colorectal rather than ovarian origin. Mismatch repair protein expression was intact, suggesting microsatellite stability. Colonoscopy subsequently revealed a large, ulcerated cecal mass; histopathology confirmed invasive colonic adenocarcinoma with mucinous features. Given the advanced stage (stage IV) at diagnosis and ongoing pregnancy, surgical intervention was deferred. A multidisciplinary team initiated systemic chemotherapy with FOLFOXIRI, which the patient tolerated well. She completed 3 cycles prior to delivery and successfully delivered a healthy infant at 31 weeks of gestation. Discussion: This case highlights the exceptional rarity of mucinous adenocarcinoma of colorectal origin in pregnancy and emphasizes the complexity of managing CRC in this setting. It emphasizes the importance of maintaining a high index of suspicion, conducting a thorough diagnostic evaluation, utilizing a multidisciplinary approach involving oncology, gastroenterology, colorectal surgery, obstetrics and neonatology is crucial to ensuring timely intervention while balancing maternal treatment with fetal well-being.