An instance of accelerated disease progression was reported in the literature following the administration of pembrolizumab in a patient diagnosed with an MMRd pituitary ACTH-secreting adenoma, showcasing the limited efficacy observed with pembrolizumab in the treatment of an ACTH-secreting pituitary adenoma characterized by mismatch repair deficiency, potentially attributable to elevated cortisol levels in the patient [50]. Here, POMC is linked to mismatch repair cancer syndrome 1.