description: An object called 'cohort'
containing a dataframe 'Muts' with the mutation status of 257 recurrently
mutated genes in cancer, a vector 'PSID' containing the patient IDs
that indexes the rows of 'Muts', a vector 'CancerType' containing
the cancer type of each row of 'Muts', a factor 'CIDs' containing
the unique cancer types in 'Muts'. Data retrieved from TCGA on November 2013