Alternating Oxaliplatin and Irinotecan Chemotherapy Combined With Capecitabine and Bevacizumab for Microsatellite-stable Stage IV Metastatic Colon Cancer With a BRAF V600E Mutation: Two Case Reports Indicating Survival Improvement over Standard Therapy.

Background/aim: Colorectal cancer (CRC) has the third-highest incidence among human cancers. Advancements in chemotherapy and targeted therapy have improved the treatment outcomes for patients with CRC. However, the management of patients with unresectable metastatic CRC (mCRC) continues to be a significant challenge for clinicians worldwide, particularly for those with microsatellite stability (MSS) and the BRAF V600E mutation, as they are associated with the poorest prognosis.

Case Reports: The present study describes two patients with unresectable MSS, BRAF V600E-mutated stage IV metastatic CRC using a biweekly alternating regimen of irinotecan and oxaliplatin combined with capecitabine and bevacizumab. Case 1 stabilized after alternating treatment, whereas Case 2 progressed after alternating treatment, with progression-free survival (PFS) of 20+ and 24.5 months, respectively. Circulating levels of carcinoemryonic antigen (CEA) dropped to near normal in both cases. A partial response (PR) was determined for both cases.

Conclusion: The two cases suggest that an alternating chemotherapy regimen of oxaliplatin and irinotecan, combined with capecitabine and bevacizumab is effective in the treatment of MSS, BRAF V600E-mutated stage IV metastatic CRC. The progression-free survival was significantly prolonged (both exceeding 20 months) compared to the first-line standard chemotherapy regimen for this disease. With a good balance between toxicity and efficacy, this alternating chemotherapy regimen can be considered as a potential first-line option for microsatellite-stable metastatic colon cancer.