title: Comparative effectiveness of chemotherapy vs resection of the primary tumour as the initial treatment in older patients with Stage IV colorectal cancer.
abstract: OBJECTIVE
  The objectives were to determine trends in the use of chemotherapy as the initial treatment and to evaluate the comparative effectiveness of initial chemotherapy vs resection of the primary tumour on survival (intention-to-treat analysis) in Stage IV colorectal cancer (CRC).
  
  
  METHODS
  This cohort study used 2000-2011 data from the Surveillance, Epidemiology, and End Results (SEER)-Medicare linked database, including patients ≥ 66 years of age presenting with Stage IV CRC. Cox proportional hazards models and instrumental variable analysis were used to compare the effectiveness of chemotherapy as the initial treatment with resection of the primary tumour as the initial treatment, with 2-year survival as the end point.
  
  
  RESULTS
  The use of chemotherapy as the first treatment increased over time, from 26.8% in 2001 to 46.9% in 2009 (P < 0.0001). The traditional Cox model showed that chemotherapy as the initial treatment was associated with a higher risk of mortality [hazard ratio (HR) = 1.35; 95% CI: 1.27-1.44]. When accounting for known and unknown confounders in an instrumental variable analysis, chemotherapy as the initial treatment suggested benefit on 2-year survival (HR = 0.68; 95% CI: 0.44-1.04); however, the association did not reach statistical significance. The study findings were similar in six subgroup analyses.
  
  
  CONCLUSIONS
  The use of chemotherapy as the initial therapy for CRC increased substantially from 2001 to 2009. Instrumental variable analysis found that, compared with resection, chemotherapy as the initial treatment offers similar or better 2-year survival in patients with Stage IV CRC. Given the morbidity and mortality associated with colorectal resection in elderly patients, chemotherapy provides an option to patients who are not good candidates for resection.
authors.affiliation: Departments of Surgery, The University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: H B
authors.initials: HB
authors.lastname: Mehta
authors.affiliation: Louisiana State University-Shreveport, Shreveport, Louisiana, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: Vargas
authors.affiliation: Departments of Surgery, The University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: D
authors.initials: D
authors.lastname: Adhikari
authors.affiliation: Departments of Surgery, The University of Texas Medical Branch, Galveston, Texas, USA.|University of South Florida, Tampa, Florida, USA.
authors.forename: F
authors.initials: F
authors.lastname: Dimou
authors.affiliation: University of Arizona, Tucson, Arizona, USA.
authors.forename: T S
authors.initials: TS
authors.lastname: Riall
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D015331:Cohort Studies; D003082:Colectomy / Q000379:methods*; D015179:Colorectal Neoplasms / Q000401:mortality / Q000473:pathology / Q000628:therapy*; D057186:Comparative Effectiveness Research; D005260:Female; D006801:Humans; D057194:Intention to Treat Analysis; D008297:Male; D009367:Neoplasm Staging; D016016:Proportional Hazards Models; D018426:SEER Program; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents
keywords: Colorectal cancer; chemotherapy; comparative effectiveness research; instrumental variable; selection bias; surgery