Synergism of Checkpoint Inhibitors and Peptide Receptor Radionuclide Therapy in the Treatment of Pituitary Carcinoma

Introduction Aggressive pituitary tumors that have progressed following temozolomide have limited treatment options. Peptide receptor radionuclide therapy and immunotherapy may have a complementary role in the management of these tumors. Methods We provide follow-up data on a previously reported patient with a hypermutated recurrent tumor. The patient in this report provided written informed consent for tumor sequencing and review of medical records on an institutional review board approved research protocol (NCT01775072). Results This patient with a corticotroph pituitary carcinoma with alkylator induced somatic hypermutation has remained on treatment with ipilimumab and nivolumab for 3.5 years and remains clinically well. After an initial partial response to checkpoint inhibitors, she has had several recurrences that have undergone immunoediting of subclonal mutations, which have been effectively treated with continuation of immunotherapy, surgery, external beam radiation, and 177Lu-DOTATATE. Following external beam RT, she had radiographic evidence of an abscopal response at a distant site of disease suggesting a synergism between checkpoint inhibitors and radiotherapy. Following treatment with 177Lu-DOTATATE, the patient had a partial response with a 61% reduction in volume of the target lesion. Conclusion In patients with aggressive pituitary tumors, treatment with checkpoint inhibitors may trigger an abscopal response from radiotherapy. With appropriate selection, an additional efficacious treatment, 177Lu-DOTATATE, may be available for a limited number of patients with aggressive pituitary adenomas, including patients who have progressed on temozolomide and exhibit increased somatostatin receptor expression on 68Ga-DOTATATE PET.