Patient description: The patient is a 60 year old man complaining of frequent headaches, generalized bone pain and difficulty chewing that started 6 years ago and is worsening. Examination shows bilateral swellings around the molars. The swellings have increased since his last examination. Several extraoral lesions are detected in the head and face. The swellings are non-tender and attached to the underlying bone. Further evaluation shows increased uptake of radioactive substance as well as an increase in urinary pyridinoline. His serum alkaline phosphatase is 300 IU/L (the normal range is 44- 147 IU/L). His family history is only significant for hypertension in his mother and DM type 2 in his father. The diagnosis of Paget's Disease of Bone was confirmed and Bisphosphonate will be started as first-line therapy.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Malignant Neoplasm Metastatic Malignant Neoplasm in the Brain Metastatic Malignant Neoplasm in the Leptomeninges Breast Cancer HER2-positive Breast Cancer Participant has treated brain and/or leptomeningeal metastases that has not recurred OR Such participants are eligible to enroll in the study and undergo leukapheresis, but they cannot start treatment with HER2-CAR T cells until there is evidence of tumor progression/recurrence Participant has recurrent brain metastases after radiation therapy OR Participant has recurrent leptomeningeal metastases after intrathecal chemotherapy OR Participant has untreated brain or leptomeningeal metastases and refuses to undergo radiation and/or intrathecal chemotherapy Note: Participants with leptomeningeal metastasis (diagnosed by positive CSF cytology or characteristic findings on brain or spine magnetic resonance imaging [MRI]) may have concomitant brain metastases, but having both is not required Participant must have a Karnofsky performance status (KPS) >= 70 Participant must have a life expectancy of >= 8 weeks The effects of HER2-CAR T cells on a developing fetus are unknown. For this reason, women of child-bearing potential must have negative serum pregnancy test and agree to use a reliable form of birth control prior to study entry and for at least two months following duration of study participation. Male research participants must agree to use a reliable form of birth control and not donate sperm during the study and for at least six months afterwards Participant has a histologically confirmed cancer which is HER2+, defined as 3+ by immunohistochemistry (IHC) or gene amplification by fluorescence in situ hybridization (FISH)  FOR STUDY Research participant requires supplemental oxygen to keep saturation greater than 95% and the situation is not expected to resolve within 2 weeks FOR STUDY Research participants with a known history of congestive heart failure (CHF) or cardiac symptoms consistent with NYHA classification III-IV within 6 months prior to day 1 of protocol treatment, cardiomyopathy, myocarditis, myocardial infarction (MI), exposure to cardiotoxic medications or with clinical history suggestive of the above must have an EKG and echocardiogram (ECHO) performed within 42 days prior to registration and as clinically indicated while on treatment Research participants with new symptoms of CHF, cardiomyopathy, myocarditis, MI, or exposure to cardiotoxic medications must have a cardiac consultation, creatinine phosphokinase (CPK), and troponin testing at pre study and as clinically indicated FOR STUDY Research participant requires dialysis FOR STUDY Research participant has uncontrolled seizure activity and/or clinically evident progressive encephalopathy FOR STUDY Failure of research participant to understand the basic elements of the protocol and/or the risks/benefits of participating in this phase 1 study. A legal guardian may substitute for the research participant FOR STUDY Participant is unwilling to stop treatment with chemotherapy or endocrine therapy during the first 3 cycles of the HER2-CAR T cell study FOR STUDY Participant has a coagulopathy or bleeding disorder or cannot safely discontinue anticoagulation prior to placement of a Rickham reservoir FOR STUDY Participant has a chronic or active viral infection of the CNS FOR STUDY Participant has any uncontrolled illness, including ongoing or active infection; participant has known active hepatitis B or C infection; participants with any signs or symptoms of active infection, positive blood cultures or radiological evidence of infections