title: Adjuvant chemotherapy for stage II right-sided and left-sided colon cancer: analysis of SEER-medicare data.
abstract: BACKGROUND
  Survival benefit from adjuvant chemotherapy is established for stage III colon cancer; however, uncertainty exists for stage II patients. Tumor heterogeneity, specifically microsatellite instability (MSI), which is more common in right-sided cancers, may be the reason for this observation. We examined the relationship between adjuvant chemotherapy and overall 5-year mortality for stage II colon cancer by location (right- vs left-side) as a surrogate for MSI.
  
  
  METHODS
  Using Surveillance, Epidemiology, and End Results (SEER)-Medicare data, we identified Medicare beneficiaries from 1992 to 2005 with AJCC stage II (n = 23,578) and III (n = 17,148) primary adenocarcinoma of the colon who underwent surgery for curative intent. Overall 5-year mortality was examined with Kaplan-Meier survival analysis and Cox proportional hazards regression with propensity score weighting.
  
  
  RESULTS
  It was found that 18 % of stage II patients (n = 2941) with right-sided cancer and 22 % (n = 1693) with left-sided cancer received adjuvant chemotherapy. After adjustment, overall 5-year survival benefit from chemotherapy was observed only for stage III patients (right-sided: hazard ratio [HR], 0.64; 95 % CI, 0.59-0.68; p < .001 and left-sided: HR, 0.61; 95 % CI, 0.56-0.68; p < .001). No survival benefit was observed for stage II patients with either right-sided (HR, 0.97; 95 % CI, 0.87-1.09; p = .64) or left-sided cancer (HR, 0.97; 95 % CI, 0.84-1.12; p = .68).
  
  
  CONCLUSIONS
  Among Medicare patients with stage II colon cancer, a substantial number receive adjuvant chemotherapy. Adjuvant chemotherapy did not improve overall 5-year survival for either right- or left-sided colon cancers. Our results reinforce existing guidelines and should be considered in treatment algorithms for older adults with stage II colon cancer.
authors.affiliation: Department of Medicine, University of Wisconsin School of Medicine and Public Health (UWSMPH), Madison, WI, USA, jmw@medicine.wisc.edu.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Weiss
authors.forename: Jessica
authors.initials: J
authors.lastname: Schumacher
authors.forename: Glenn O
authors.initials: GO
authors.lastname: Allen
authors.forename: Heather
authors.initials: H
authors.lastname: Neuman
authors.forename: Erin O'Connor
authors.initials: EO
authors.lastname: Lange
authors.forename: Noelle K
authors.initials: NK
authors.lastname: Loconte
authors.forename: Caprice C
authors.initials: CC
authors.lastname: Greenberg
authors.forename: Maureen A
authors.initials: MA
authors.lastname: Smith
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D017024:Chemotherapy, Adjuvant; D044682:Colon, Ascending; D044683:Colon, Descending; D012809:Colon, Sigmoid; D044684:Colon, Transverse; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D009367:Neoplasm Staging; D018426:SEER Program / Q000706:statistics & numerical data; D015996:Survival Rate; D014481:United States / Q000453:epidemiology