Patient description: The patient is a 16-year-old girl recently diagnosed with myasthenia gravis, class IIa. She complains of diplopia and weakness affecting in her upper extremities. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She is on acetylcholinesterase inhibitor treatment combined with immunosuppressants. But she still has some symptoms. She does not smoke or use illicit drugs. She is not sexually active, and her menses are regular. Her physical exam and lab studies are not remarkable for any other abnormalities. BP: 110/75 Hgb: 11 g/dl WBC: 8000 /mm3 Plt: 300000 /ml Creatinine: 0.5 mg/dl BUN: 10 mg/dl Beta hcg: negative for pregnancy

Clinical trial eligibility criteria: eligible ages (years): 2.0-30.0,  Adrenal Cortex Carcinoma Alveolar Soft Part Sarcoma Central Nervous System Neoplasm Childhood Clear Cell Sarcoma of Soft Parts Clear Cell Sarcoma of Soft Tissue Ewing Sarcoma Hepatoblastoma Hepatocellular Carcinoma Osteosarcoma Recurrent Adrenal Cortex Carcinoma Recurrent Alveolar Soft Part Sarcoma Recurrent Ewing Sarcoma Recurrent Hepatoblastoma Recurrent Hepatocellular Carcinoma Recurrent Malignant Solid Neoplasm Recurrent Osteosarcoma Recurrent Primary Malignant Central Nervous System Neoplasm Recurrent Renal Cell Carcinoma Recurrent Rhabdomyosarcoma Recurrent Soft Tissue Sarcoma Recurrent Thyroid Gland Medullary Carcinoma Refractory Ewing Sarcoma Refractory Malignant Solid Neoplasm Refractory Osteosarcoma Refractory Primary Malignant Central Nervous System Neoplasm Refractory Rhabdomyosarcoma Refractory Soft Tissue Sarcoma Renal Cell Carcinoma Rhabdomyosarcoma Solid Neoplasm Thyroid Gland Medullary Carcinoma Wilms Tumor Upper age limit of =< 18 years of age for medullary thyroid carcinoma (MTC), renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC) Patients must have a body surface area >= 0.35 m^2 Patients must have recurrent or refractory disease, or newly diagnosed disease with no known curative therapy or therapy proven to prolong survival with an acceptable quality of life; patients must have had histologic verification of one of the malignancies listed below at original diagnosis or at relapse Ewing sarcoma Rhabdomyosarcoma (RMS) Non-rhabdomyosarcoma soft tissue sarcomas (STS) including microphthalmia transcription factor associated STS (alveolar soft part sarcoma [ASPS] and clear cell sarcoma [CCS]) Osteosarcoma Wilms tumor Rare tumors Medullary thyroid carcinoma (MTC)  Pregnant or breast-feeding women will not be entered on this study due to risks of fetal and teratogenic adverse events as seen in animal/human studies; pregnancy tests must be obtained in girls who are post-menarchal; males or females of reproductive potential may not participate unless they have agreed to use two methods of birth control a medically accepted barrier method of contraceptive method (e.g., male or female condom) and a second effective method of birth control-during protocol therapy and for at least 4 months after the last dose of XL184; abstinence is an acceptable method of birth control Growth factors that support platelet or white cell number or function must not have been administered within the 7 days prior to enrollment (14 days if pegfilgrastim) Patients requiring corticosteroids who have not been on a stable or decreasing dose of corticosteroid for the 7 days prior to enrollment are not eligible; if used to modify immune adverse events related to prior therapy, >= 14 days must have elapsed since last dose of corticosteroid Previous treatment with XL184 (cabozantinib) or another MET/HGF inhibitor (tivantinib, crizotinib) Patients who are currently receiving another investigational drug are not eligible Patients who are currently receiving other anti-cancer agents are not eligible Patients who are receiving cyclosporine, tacrolimus or other agents to prevent either graft-versus-host disease post bone marrow transplant or organ rejection post-transplant are not eligible for this trial Patients must not be receiving any of the following potent CYP3A4 inducers or inhibitors: erythromycin, clarithromycin, ketoconazole, azithromycin, itraconazole, grapefruit juice or St. John's wort Concomitant anticoagulation with oral anticoagulants (e.g., warfarin, direct thrombin, and Factor Xa inhibitors) or platelet inhibitors (e.g., clopidogrel) are prohibited