In a 46‑year‑old woman with Eastern Cooperative Oncology Group performance status 1 presenting with subacute intestinal obstruction from a sigmoid colon adenocarcinoma adherent to the anterior uterus and a solitary 1.8 cm hypodense liver lesion, what is the recommended next management?

Management of Sigmoid Adenocarcinoma with Subacute Obstruction and Suspected Liver Metastasis

The next step is to create a diverting stoma (preferably transverse colostomy) to relieve the obstruction, followed by complete staging including liver biopsy or PET-CT to characterize the liver lesion, comprehensive molecular testing (MMR/MSI, RAS, BRAF, HER2), and then initiate neoadjuvant chemotherapy if the liver lesion is confirmed metastatic, reserving definitive resection until after systemic therapy. 1, 2

Immediate Management: Decompressive Stoma

Avoid immediate tumor resection in this obstructive presentation. The sigmoid tumor with uterine involvement represents locally advanced disease requiring multimodal therapy, and attempting primary resection in an obstructed, unprepared bowel significantly increases morbidity and mortality. 1

• Fashion a diverting stoma to relieve the obstruction and permit proper staging and oncologic treatment planning. 1
• Transverse colostomy is the preferred option as it provides long-term decompression through the entire neoadjuvant treatment period without interfering with therapeutic schedules. 1
• Loop ileostomy is an alternative, but transverse colostomy offers better durability for the extended treatment timeline ahead. 1
• Do not use self-expanding metal stents (SEMS) in this rectosigmoid location, as they are associated with chronic pain, tenesmus, and increased risk of perforation during subsequent chemotherapy and radiation, which could compromise oncologic outcomes. 1

Critical Staging Requirements

Characterize the Liver Lesion

The 1.8 cm hypodense liver lesion must be definitively characterized before finalizing the treatment plan. 2

• MRI of the liver is the preferred imaging modality to accurately define whether this represents a metastasis or a benign lesion. 2, 3
• If MRI is equivocal, consider PET-CT or image-guided biopsy of the liver lesion. 2
• The distinction between stage III (locally advanced without distant metastases) versus stage IV (metastatic) disease fundamentally changes the treatment algorithm. 2

Comprehensive Molecular Testing

Obtain molecular profiling immediately as it will guide systemic therapy selection. 2

• MMR/MSI status is mandatory - if dMMR/MSI-high, immune checkpoint inhibitors become highly effective first-line options for metastatic disease. 2
• RAS mutation testing (KRAS and NRAS) is required before considering anti-EGFR therapy. 2
• BRAF V600E mutation status - if positive, targeted therapy with encorafenib plus cetuximab may be appropriate. 2
• HER2 amplification testing should be performed. 2
• DPD deficiency testing to avoid fluoropyrimidine toxicity. 2

Treatment Algorithm Based on Staging

Scenario A: If Liver Lesion is Benign (Stage III Disease)

Proceed with neoadjuvant chemoradiotherapy followed by definitive surgery. 1

• The tumor adherent to the uterus represents locally advanced disease (likely T4b) requiring neoadjuvant combined modality therapy to improve resectability and local control. 1
• Standard neoadjuvant regimen: fluoropyrimidine-based chemoradiotherapy for 5-6 weeks. 1
• After 6-8 weeks post-chemoradiation, perform en bloc resection of sigmoid colon with anterior uterus if curative resection is achievable. 1, 2
• The stoma remains in place during neoadjuvant therapy and can be reversed at the time of definitive resection or as a staged procedure. 1

Scenario B: If Liver Lesion is Metastatic (Stage IV Disease)

Initiate systemic chemotherapy with intent to convert to resectable disease (conversion chemotherapy). 1, 2, 4

• First-line regimen: FOLFOX or FOLFIRI plus bevacizumab is the standard approach. 2
• If RAS/BRAF wild-type with left-sided primary, consider anti-EGFR antibody (cetuximab or panitumumab) instead of bevacizumab. 2
• If BRAF-mutated, consider encorafenib plus cetuximab. 2
• If dMMR/MSI-high, immune checkpoint inhibitors (pembrolizumab or nivolumab) are highly effective first-line options with superior outcomes. 2

Reassess resectability after 2-3 months of chemotherapy. 1, 4

• If both the liver metastasis and primary tumor become resectable with good response to chemotherapy, consider synchronous or staged resection of both sites. 1, 2, 4
• For liver metastasis resection, technical requirements include R0 resection with 1 cm margins and preservation of >30% residual normal liver. 2, 3
• The primary sigmoid tumor with uterine involvement would require en bloc resection including anterior uterus to achieve negative margins. 1, 2
• Approximately 13% of initially unresectable colorectal liver metastases can be converted to resectable with modern chemotherapy. 1

Critical Pitfalls to Avoid

Do not perform emergency resection of the obstructing primary tumor. This approach in an unprepared, obstructed bowel with locally advanced disease requiring multimodal therapy significantly increases perioperative morbidity and prevents optimal oncologic management. 1

Do not assume the liver lesion is metastatic without tissue diagnosis or definitive imaging. A significant proportion of hypodense liver lesions in this context may be benign (cysts, hemangiomas), and misclassification would lead to inappropriate systemic therapy instead of curative-intent local therapy. 2, 3

Do not use bevacizumab if planning surgery within 6-8 weeks due to increased risk of bleeding, wound complications, and anastomotic leak. 1

Ensure adequate lymph node harvest (minimum 12 nodes) at definitive resection for proper staging and prognostic assessment. 2, 3

Adjuvant Therapy Considerations

If definitive resection is achieved:

• For stage III disease (node-positive): 6 months of FOLFOX or CAPOX is standard adjuvant therapy. 2
• For stage II disease with high-risk features (T4, inadequate lymph node sampling, obstruction at presentation): consider adjuvant chemotherapy. 2
• For resected stage IV disease: complete the planned perioperative chemotherapy course (typically 6 months total perioperative therapy). 2