Treatment Adherence to Adjuvant Chemotherapy According to the New Standard 3-month CAPOX Regimen in High-risk Stage II and Stage III Colon Cancer: A Population-based Evaluation in The Netherlands.

Background: A 3-month adjuvant treatment regimen with capecitabine and oxaliplatin (CAPOX) for high-risk stage II (T4N0) and stage III (node-positive) colon cancer was implemented in the Netherlands in 2017. The IDEA trial showed a clinically irrelevant difference in long-term outcomes in combination with a substantial decrease in toxicity in comparison with a 6-month regimen. A significantly increased dose intensity was observed in the 3-month arm, which might be essential to achieve optimal long-term outcomes. Hence, the aim of the present study was to evaluate if a similar dose intensity could be achieved in patients treated with adjuvant CAPOX for 3 months in daily practice.

Materials and methods: Patients scheduled for 3 months of adjuvant CAPOX for high-risk stage II or stage III colon cancer were selected from the Netherlands Cancer Registry. The number of administered cycles and the daily cumulative dose of capecitabine and oxaliplatin were extracted from the medical files. Relative dose intensity (RDI) was determined by comparing the administered dose intensity with the standard dose intensity.

Results: In total, 802 (80.0%) of the 1002 patients completed 4 cycles of CAPOX. The overall mean RDI of adjuvant treatment was 82.9% for capecitabine, and 83.8% for oxaliplatin, based on the combination of dose reductions and omitting cycles.

Conclusion: One out of 5 patients did not complete 4 cycles of CAPOX. The administered dose of capecitabine and oxaliplatin in the first year after the update of the guideline was lower than the advised dose for the 3-month CAPOX regimen, and the administered dose in the IDEA study. The impact on long-term oncological outcomes should be awaited.