How do you decide between Nivolumab + Ipilimumab and Pembrolizumab or Nivolumab monotherapy in later lines of MSI-H Colorectal cancer?

The data are fairly clear that patients with the combination of nivolumab and ipilimumab is highly active based on the Checkmate-142 study (Overman, et al, JCO 36, no. 8 (March 10 2018): 773-779, 2018) showing a 55% RR with 5% CR (n=119 patients, all post at least 2 prior chemo regimens). PFS at 12 months was 71% and 12-month survival was 85%. Compared to the single agent nivo cohort of this study, this combination showed substantially improved PFS and survival with somewhat higher RR. Ipi is given at 1 mg/kg for 4 doses. Therefore, there is some increased immuno-toxicity with the ipi combination, but at the lower dose, it is only moderately increased. I believe this combo would be appropriate outside of studies if the patient is in good ge...