How would you use Oncotype for adjuvant colon cancer treatment decisions?

Oncotype is an RNA expression profile validated in multiple prospective phase 3 trials. It is mainly validated for stage II colon cancer, but data for stage III also exist from NSABP C0-7. Since the stage II data is prognostic, not predictive it does not give the benefit of treatment (though data from CO-7 gives outcomes with treatment).

The prognostic data can be helpful in stage II to specifically determine the individual patient Recurrence Risk (RR), rather than the overall stage II risk of 15% recurrence.  From this individual RR, one can extrapolate the potential benefit of adjuvant chemotherapy.  For those with low risk (10-15%) the Oncotype can be helpful in deciding not to recommend adjuvant therapy.  I find this particularly useful for those whom I am not enthusiastic about administering adjuvant therapy.  This is a reasonably large group.  

Conversely for those few patients with high RR, which may be equal to stage III CRC (25-30%), adjuvant therapy can be recommended with greater confidence, be it with single agent fluoropyrimidine or a FP-oxaliplatin doublet. I find this helpful in those patients who are reluctant to consider adjuvant therapy.  If the patient is quite adamant that they would like therapy even for a 2% or greater relative benefit in survival Oncotype may not be useful.  Similarly if a patient definitely would not consider treatment, even if they have a high RR, I likewise do not order the Oncotype DX Colon test.