Patient description: A 16-year-old girl came to the clinic complaining of weight gain and abnormal menstrual cycles. Her BMI was 24, but she has gained 5 kg in the past few weeks. She gets tired more frequently and does not have energy to go dancing with her friends. Her lab results were remarkable for high TSH levels (15 mU/L) and low free T4 levels (0.18 ng/dl). Her anti-TPO levels were extremely high (136 IU/ml). She was diagnosed with Hashimoto disease. She does not smoke and she is not sexually active.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  BRAF NP_004324.2:p.V600M BRAF V600E Mutation Present Metastatic Thyroid Gland Carcinoma Refractory Thyroid Gland Carcinoma Stage IV Differentiated Thyroid Gland Carcinoma AJCC v8 Stage IVA Differentiated Thyroid Gland Carcinoma AJCC v8 Stage IVB Differentiated Thyroid Gland Carcinoma AJCC v8 Ability to understand and the willingness to sign a written informed consent document Histologically (or cytologically) confirmed diagnosis of metastatic, radioiodine (RAI) refractory, BRAFV600E/M mutant differentiated thyroid cancer (DTC) Note: RAI refractoriness is defined as The absence of uptake of RAI on either a low-dose diagnostic whole body scan, or a post-treatment RAI scan in measurable lesions Radiographic progression of disease within 12 months of the last course of RAI treatment, or Having a cumulative lifetime administered dose of > 600 mCi of RAI Measurable disease meeting the following and confirmed by radiography review At least 1 lesion of >= 1.0 cm in the longest diameter for a non-lymph node or > 1.5 cm in the short-axis diameter for a lymph node metastasis that is serially measurable according to Response Evaluation in Solid Tumors (RECIST) 1.1 using computed tomography/magnetic resonance imaging (CT/MRI). If there is only 1 target lesion and it is a non-lymph node, it should have a longest diameter of >= 1.5 cm Lesions that have had external beam radiotherapy or locoregional therapies such as radiofrequency (RF) ablation must show evidence of progressive disease based on 1.1 to be deemed a target lesion Eastern Cooperative Oncology Group (ECOG) performance status =< 1  Currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy or used an investigational agent/device within 4 weeks of first dose of study intervention Note: Individuals in the follow-up phase of a prior investigational study may participate as long as it has been 4 weeks since last dose of the previous investigational agent of device Participants with active, known, or suspected autoimmune disease. Participants with type I diabetes mellitus, residual hypothyroidism due to autoimmune thyroiditis only requiring hormone replacement, skin disorders (such as vitiligo, psoriasis, or alopecia) not requiring systemic treatment are permitted to enroll Prior treatment with selective/potent BRAF/MEK inhibitors including vemurafenib, dabrafenib, encorafenib, selumetinib, trametinib, cobimetinib, binimetinib Note: Prior therapy with oral multikinase inhibitors (e.g., lenvatinib, sorafenib, cabozantinib, pazopanib, sunitinib, etc.) remain eligible for study participation Prior treatment with anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or anti-CTLA-4 antibody (including ipilimumab or any other antibody or drug specifically targeting T cell co-stimulation or immune checkpoint pathways) Participants with a condition requiring systemic treatment with either corticosteroids (>= 10 mg daily prednisone or equivalent) or other immunosuppressive medications within 14 days of study drug administration. Inhaled or topical steroids are permitted in the absence of active autoimmune disease History of allergy or hypersensitivity to any monoclonal antibody History or current evidence of retinal vein occlusion (RVO) or current risk factors to RVO (e.g. uncontrolled glaucoma or ocular hypertension, history of hyperviscosity or hypercoagulability syndromes); history of retinal degenerative disease Previous or concurrent malignancy within 3 years of study entry, with the following exceptions