The 21-gene recurrence score (Oncotype DX: RS) appears to augment 
clinico-pathologic prognostication and is predictive of adjuvant chemotherapy 
benefit in node-negative (N-) and node-positive (N+), endocrine-sensitive breast 
cancer. RS is a costly assay that is associated with good 'value for money' in 
N- disease, while economic evaluations in N+ disease based on most recent data 
have not been conducted. We examined the cost-utility (CU) of a RS-guided 
adjuvant strategy, compared to current practice without RS in N- and N+, 
endocrine-sensitive, breast cancer from a Canadian health care system 
perspective. A generic state-transition model was developed to compute 
cumulative costs and quality-adjusted life years (QALYs) over a 25-year horizon. 
Patient outcomes with and without chemotherapy in RS-untested cohorts and in 
those with low, intermediate and high RS were examined based on the reported 
prognostic and predictive impact of RS in N- and N+ disease. Chemotherapy 
utilization (current vs. RS-guided), unit costs and utilities were derived from 
a Nova Scotia Canadian population-based cohort, local unit costs and the 
literature. Costs and outcomes were discounted at 3% annually, and costs were 
reported in 2011 Canadian dollars ($). Probabilistic and one-way sensitivity 
analyses were conducted for key model parameters. Compared to a non-RS-guided 
strategy, RS-guided adjuvant therapy was associated with $2,585 and $864 
incremental costs, 0.27 and 0.06 QALY gains, and resultant CUs of $9,591 and 
$14,844 per QALY gained for N- and N+ disease, respectively. CU estimates were 
robust to key model parameters, and were most sensitive to chemo utilization 
proportions. RS-guided adjuvant therapy appears to be a cost-effective strategy 
in both N- and N+, endocrine-sensitive breast cancer with resultant CU ratios 
well below commonly quoted thresholds.