title: The influence of 21-gene recurrence score assay on chemotherapy use in a population-based sample of breast cancer patients.
abstract: To quantify the influence of RS assay on changing chemotherapy plans in a general practice setting using causal inference methods.
  
  
  
  We surveyed 3880 newly diagnosed breast cancer patients in Los Angeles and Georgia in 2013-14. We used inverse propensity weighting and multiple imputations to derive complete information for each patient about treatment status with and without testing.
  
  
  
  A half of the 1545 women eligible for testing (ER+ or PR+, HER2-, and stage I-II) received RS. We estimate that 30% (95% confidence interval (CI) 10-49%) of patients would have changed their treatment selections after RS assay, with 10% (CI 0-20%) being encouraged to undergo chemotherapy and 20% (CI 10-30%) being discouraged from chemotherapy. The subgroups whose treatment selections would be changed the most by RS were patients with positive nodes (44%; CI 24-64%), larger tumor (43% for tumor size >2 cm; CI 23-62%), or younger age (41% for <50 years, CI 23-58%). The assay was associated with a net reduction in chemotherapy use by 10% (CI 4-16%). The reduction was much greater for women with positive nodes (31%; CI 21-41%), larger tumor (30% for tumor size >2 cm; CI 22-38%), or younger age (22% for <50 years; CI 9-35%).
  
  
  
  RS substantially changed chemotherapy treatment selections with the largest influence among patients with less favorable pre-test prognosis. Whether this is optimal awaits the results of clinical trials addressing the utility of RS testing in selected subgroups.
authors.affiliation: University of Michigan, Department of Biostatistics.
authors.forename: Yun
authors.initials: Y
authors.lastname: Li
authors.affiliation: Stanford University, Departments of Medicine and Health Research and Policy.
authors.forename: Allison W
authors.initials: AW
authors.lastname: Kurian
authors.affiliation: University of Michigan, Department of Biostatistics.
authors.forename: Irina
authors.initials: I
authors.lastname: Bondarenko
authors.affiliation: University of Michigan, Department of Biostatistics.
authors.forename: Jeremy M G
authors.initials: JMG
authors.lastname: Taylor
authors.affiliation: University of Michigan, Department of Radiation Oncology.
authors.forename: Reshma
authors.initials: R
authors.lastname: Jagsi
authors.affiliation: Emory University, Department of Epidemiology.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Ward
authors.affiliation: University of Southern California, Keck School of Medicine.
authors.forename: Ann S
authors.initials: AS
authors.lastname: Hamilton
authors.affiliation: University of Michigan, Department of Internal Medicine.|University of Michigan, Department of Health Management and Policy.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Katz
authors.affiliation: University of Michigan, Department of Internal Medicine.|Ann Arbor Veterans Affairs Medical Center.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Hofer
mesh_terms: D000328:Adult; D000368:Aged; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000235:genetics*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000453:epidemiology / Q000235:genetics* / Q000473:pathology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D060787:Neoplasm Grading; D009362:Neoplasm Metastasis; D009364:Neoplasm Recurrence, Local / Q000235:genetics*; D009367:Neoplasm Staging; D000071185:Pharmacogenomic Testing / Q000379:methods; D012307:Risk Factors; D018426:SEER Program; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor
keywords: 21-gene recurrence score assay; Breast cancer; Chemotherapy; Population studies