Patient description: The patient is a 33-year-old woman complained of fatigue, weight gain and abnormal spotting between menses. No hirsutism or nipple discharge was detected. Her BMI was 34. Her lab results were remarkable for high TSH level (13 mU/L) and low free T4 level (0.2 ng/dl). Her anti-TPO levels were extremely high (120 IU/ml). She was diagnosed with Hashimoto's thyroiditis. Her aunt, brother and mother have the same disease. After starting 250 mcg Levothyroxine per day, her symptoms improved significantly and her periods are normal. She is still overweight with BMI of 31. Her most recent thyroid profile revealed all results except for anti-TPO within the normal range: TSH: 2.35 mU/L Free T4: 2.7 ng/dl Anti-TPO: 75 IU/ml

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Malignant Melanoma, Metastatic Histologically confirmed diagnosis of melanoma Stage III or stage IV metastatic melanoma Disease that is measurable. This is defined as lesions measuring at least 10mm on radiologic imaging. For lymph node disease, the lesion must measure at least 15 mm or have been biopsied and shown to contain melanoma. Skin or mucosal lesions that are not measurable on radiologic imaging but measure at least 10mm on clinical exam are also acceptable. (See Section 13.2 for detailed definition of measurable disease) Disease is termed unresectable or the patient refuses resection The Eastern Cooperative Oncology Group (ECOG) performance status of 1 or better Age ≥18 years. This is due to the limited data with pembrolizumab in children younger than 18 years of age Normal organ and marrow function as defined below Aspartate aminotransferase (AST) (SGOT) or alanine aminotransferase (ALT) (SGPT) ≤2.5 × institutional upper limit of normal (≤5 x upper limit of normal for patient with liver metastasis) Total bilirubin within 1.5 x institutional level of normal or direct bilirubin ≤ upper limit of normal (ULN) for patient with total bilirubin levels > 1.5 ULN) Hemoglobin ≥ 9.0g/dL or ≥5.6mmol/L  Prior therapy with anti-PD-1 antibody The patient has symptomatic brain metastases. Asymptomatic brain metastases are permitted provided that there is no steroid requirement, no more than 4 metastases detected on standard MRI imaging, no metastatic brain lesion that is > 3 cm in size, and no lepto-meningeal disease Patient has not recovered to Grade 0-1 from adverse events due to prior chemotherapy, radiation, or biological cancer therapy (including monoclonal antibody (mAb)) The patient is not recovered from minor or major surgery and is less than 4 weeks from major surgery prior to starting treatment with pembrolizumab Significant auto-immune disease requiring hospitalization within the past two years or any history of life-threatening auto-immune disease Immunosuppressive therapy including systemic corticosteroids except for maintenance dosing for adrenal insufficiency Concurrent use of any other investigational agents Active central nervous system metastasis and/or carcinomatous meningitis causing symptoms Known additional malignancy that is progressing or requires active treatment with the exceptions of basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or in situ cervical cancer that has undergone potentially curative therapy Active autoimmune disease or a syndrome that requires systemic steroids or immunosuppressive agents with the exceptions of replacement dose steroids for adrenal insufficiency, vitiligo, resolved childhood asthma/atopy, intermittent use of inhaled steroids, local steroid injections, hypothyroidism stable on hormone replacement, and Sjogren's syndrome