Furthermore, recent research has shown promise for alternative markers of response, including tumor-infiltrating immune cell [16, 17], expression of indoleamine 2, 3-dioxygenase (IDO), microbiome profile, mutational load, mismatch repair deficiency (dMMR), expression of inflammatory genes [18] baseline metabolic tumor volume [19], body mass index [20], smoking status [21] and concomitant medications [22]. Here, IDO1 is linked to neoplasm.