Neurofibromatosis Type 1 Tumor Early Detection Study

The goal of this observational study is to determine if a liquid biopsy (i.e. blood test) is an effective clinical tool for monitoring the development of malignant peripheral nerve sheath tumor (MPNST) among adults (18 years and older) with Neurofibromatosis Type 1 (NF1), compared to the current standard of care. The main questions it aims to answer are: How effective is liquid biopsy compared to the current standard of care (clinical surveillance and imaging) for early detection of MPNST development among people with NF1? Can liquid biopsy offer a cost-effective method for early detection of MPNST in people with NF1? Also, can liquid biopsy provide earlier detection that potentially leads to better outcomes? Also, can offering liquid biopsy improve access to care for people experiencing barriers to access (such as minority populations or people in rural areas)? At baseline, participants will be asked to: * Complete surveys to provide their demographic and NF1-related health information. * Report whether or not they are experiencing MPNST-related symptoms. * Provide blood samples (15 mL blood total between three tubes, which is approximately one tablespoon). Every six months during the five-year follow-up period, participants will be asked to: * Complete additional surveys to report whether or not they are experiencing MPNST-related symptoms and/or if they have been diagnosed with a new MPNST. * Provide an additional blood sample (10 mL blood total in one tube). If diagnosed with an MPNST by their healthcare provider during the follow-up period, participants will be asked to: * Complete an additional survey regarding their diagnosis and symptoms. * Provide an additional blood sample (10 mL blood in one tube). * In parallel, the study team will request a sample of tumor tissue from the care provider, if available.