Ascertainment of treatment

Administrative codes identified cancer-directed treatments (Appendix A) and have high validity for identifying specific chemotherapy agents.[30-32] Postoperative chemotherapy was assessed from the date of surgery through the following 122 days (4 months). Specific chemotherapeutic agents administered within the 60 days of the first chemotherapy administration were used to define the initial postoperative chemotherapy group (i.e., 5-FU/capecitabine alone or in combination with oxaliplatin).[30, 33-35]