SEOM Clinical Guidelines for Localized Rectal Cancer

The SEOM (Spanish Society of Medical Oncology) Clinical Guidelines for localized rectal cancer emphasize a comprehensive, multidisciplinary approach to ensure optimal treatment outcomes. Below is a detailed overview based on the context provided:

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### **1. Accurate Staging Is Critical**

• **Pelvic MRI** is the gold standard for staging localized rectal cancer. It provides detailed information on tumor depth, nodal involvement, circumferential resection margin (CRM) status, mesorectal fascia involvement, and extramural venous invasion (EMVI).
• Accurate staging is essential for determining prognosis and guiding treatment strategies.

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### **2. Multidisciplinary Management**

• All cases of rectal cancer should be discussed in a **multidisciplinary tumor board**. This ensures coordinated input from oncologists, radiologists, surgeons, and pathologists, leading to individualized treatment plans and improved outcomes.

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### **3. Universal MMR/MSI Testing**

• **Mismatch repair (MMR) or microsatellite instability (MSI) testing** is mandatory for all newly diagnosed rectal cancer patients. Results are critical for assessing prognosis and determining eligibility for immunotherapy, especially in cases of deficient mismatch repair (dMMR).

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### **4. Tumor Location and Classification**

• Rectal cancers are classified based on their distance from the anal verge into **low**, **middle**, or **high** rectal tumors.
• Tumor location impacts surgical options (e.g., sphincter preservation) and the feasibility of organ-preserving strategies.

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### **5. Early-Stage Disease Management**

• For **early-stage disease** (e.g., pT1 tumors with favorable histology), **local excision** or **endoscopic approaches** may be considered. However, a meticulous histopathologic risk assessment is required to ensure safe management.

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### **6. Standard Surgical Approach: Total Mesorectal Excision (TME)**

• **Total Mesorectal Excision (TME)** is the standard curative surgical technique for localized rectal cancer. When performed with high technical quality, TME minimizes local recurrence and optimizes oncologic outcomes.

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### **7. Neoadjuvant Therapy Options**

• **Total Neoadjuvant Therapy (TNT)** is increasingly used for locally advanced rectal cancer. It combines chemotherapy and radiation before surgery to:
• Improve tumor response.
• Reduce distant recurrence risk.
• Enable organ preservation strategies in cases of complete clinical response.

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### **8. Organ Preservation and Watch-and-Wait Strategies**

• TNT can lead to **complete clinical response**, making **nonoperative management** a viable option for selected patients. This avoids surgery and preserves rectal function.
• The **Watch-and-Wait approach** is considered safe for patients with documented complete response, with outcomes comparable to immediate surgery. Intensive surveillance protocols are required to monitor for regrowth.

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### **9. Radiotherapy Personalization**

• Radiotherapy options include **short-course** or **long-course regimens**, tailored to tumor risk and location. Care must be taken to avoid overtreatment in low-risk cases.

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### **10. Chemotherapy Sequencing**

• **Consolidation chemotherapy** after chemoradiation increases complete response rates and enhances the feasibility of organ preservation.

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### **11. High-Risk Disease Management**

• Patients with high-risk features (e.g., threatened margins, EMVI, or nodal involvement) benefit most from **TNT**. Risk-adapted treatment intensification improves disease control and reduces recurrence.

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### **12. Limited Role of Adjuvant Chemotherapy**

• After modern neoadjuvant therapy approaches, **adjuvant chemotherapy** offers modest benefits. Its use should be individualized based on patient risk factors and response to prior treatment.

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### **13. Immunotherapy for dMMR Rectal Cancer**

• **Checkpoint inhibitors** (e.g., PD-1/PD-L1 inhibitors) demonstrate dramatic responses in patients with dMMR rectal cancer. In selected cases, immunotherapy may replace chemoradiation.

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### **14. Elderly and Frail Patients**

• Treatment decisions for older or frail individuals should prioritize **quality of life**. A comprehensive geriatric assessment is recommended to tailor therapies to the patient's overall health and functional status.

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### **15. Local Excision Post-Neoadjuvant Therapy**

• For small residual tumors after neoadjuvant therapy, **local excision** may reduce morbidity compared to radical surgery. This approach is reserved for carefully selected patients.

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### **16. Long-Term Survivorship Care**

• Survivorship care should address:
• **Recurrence surveillance**.
• Management of functional outcomes and quality of life.
• Lifestyle counseling and symptom management.

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### **Key Takeaways**

• **Personalized treatment** based on tumor staging, location, and risk factors is essential.
• **TNT** and organ preservation strategies are revolutionizing rectal cancer management.
• **Multidisciplinary care** and intensive surveillance protocols are critical for optimizing outcomes.
• Emerging therapies like **immunotherapy** are transforming care for dMMR rectal cancer.

The SEOM guidelines align with international standards, emphasizing evidence-based, patient-centered approaches to ensure the best oncologic and functional outcomes for localized rectal cancer patients.