Practice Variation in the Adjuvant Treatment of Colon Cancer in the Netherlands: A Population-based Study

Background/Aim: Adjuvant chemotherapy is recommended for a subgroup of colon cancer patients based on patient and tumour characteristics. Population-based data on the adoption of the prevailing guideline recommendations including the assessment of tumour mismatch repair (MMR) status are limited, while variations in treatment strategies may influence patient outcomes. Therefore, the aim of the study was to assess practice variation in adjuvant chemotherapy administration in colon cancer patients. Patients and Methods: We examined the association between patient, demographic and tumour characteristics on the odds of being treated with adjuvant chemotherapy in a random sample of adult stage IIIII colon cancer patients from the Dutch National Cancer Registry (2008-2015) and assessed its association with survival. Results: The study population consisted of 2,044 patients of whom 18% (79 out of 450) were high-risk stage II and 65% (645 out of 997) were stage III colon cancer and received adjuvant chemotherapy. Chemotherapy administration differed between individual hospitals (high-risk stage II: 0-39%; p=0.01; stage III: 50-78%; p=0.06). Type of hospital (teaching versus academic) and the presence of a pT4 tumour were positively associated (high-risk stage II), and bowel perforation and examined regional lymph nodes (<10) were negatively associated (stage III) with adjuvant treatment. Higher age was associated with non-administration of adjuvant chemotherapy for both stages. Tumour MMR-status assessment increased from 9% to 23% (p<0.001), but 62% of high-risk stage II and 13% of stage III patients did not undergo guideline-recommended MMR-status testing. Adjuvant chemotherapy was correlated with survival for stage III (HR=0.4; 95%CI=0.3-0.5) but not for high-risk stage II patients (HR=1.2; 95%CI=0.7-2.2). Conclusion: Significant practice variation in the adjuvant treatment of colon cancer on hospital level was demonstrated, predominantly in high-risk stage II patients. The implementation of MMR testing was suboptimal. We recommend continuous monitoring of treatment patterns using population-based data, which should facilitate hospital auditing and improve guideline implementation and quality of care for colon cancer patients.