The results of the RMC cohort of a phase 2 clinical trial conducted at the University of Texas MD Anderson Cancer Center suggest that anti-PD1 immune checkpoint therapy with pembrolizumab does not demonstrate clinical benefit in patients with RMC. All 5 patients with RMC had rapid disease progression despite pembrolizumab treatment, with a median time to progression of 8.7 weeks. Further accrual in this cohort was halted due to the observed lack of efficacy and aggressive clinical and radiological progression. PD-L1 expression and tumor-infiltrating lymphocyte (TIL) levels were not associated with clinical benefit.