Adult patients with primary or secondary central nervous system malignancies will be invited to undergo a baseline [C-11]-CS1P1 PET scan and a follow-up scan within 24 months of the baseline scan (preferably within 6-months post-treatment).The study will describe patterns of tracer uptake in tumors and normal brain and explore how these patterns relate to MRI findings, treatments received, and clinical outcomes.

This is a prospective, single-arm interventional imaging study designed to evaluate the investigational PET radiotracer [C-11]-CS1P1 in adults with primary or secondary central nervous system malignancies. [C-11]-CS1P1 PET may provide complementary information about disease activity, treatment response, and the tumor microenvironment in central nervous system cancers.

Eligible participants will be adults with confirmed primary central nervous system tumors (for example, gliomas) or secondary central nervous system involvement (brain metastases or other CNS metastases). After providing informed consent, participants will undergo a baseline [C-11]-CS1P1 PET scan in addition to their routine clinical imaging. The PET scan will be performed on a PET/CT or PET/MR scanner following intravenous administration of [C-11]-CS1P1, using a standardized acquisition protocol for brain imaging. Participants will be monitored for adverse events related to tracer administration and radiation exposure, which are expected to remain within accepted research limits.

Participants will be invited to return for one follow-up [C 11]-CS1P1 PET scan within 24 months of the baseline scan, preferably within approximately 6 months after treatment. Follow up imaging will allow assessment of longitudinal changes in [C 11]-CS1P1 uptake in relation to treatment and disease course. Clinical management will not be altered by participation in this study.

Quantitative PET parameters (for example, standardized uptake values, tumor to background ratios, and volumetric measures) will be derived from tumor and normal appearing brain. Qualitative assessments of tracer uptake patterns will also be performed. These PET measures will be compared with MRI characteristics, treatment history, and available clinical outcomes (including radiographic progression and survival) to explore the potential of [C 11]-CS1P1 PET as a diagnostic biomarker of tumor activity and treatment response in central nervous system malignancies. This exploratory study is intended to generate preliminary data that may inform the design of future trials using [C 11]-CS1P1 PET in this patient population.

Inclusion Criteria:

• Male or female, any race
• Age ≥ 18 years
• Capable of providing written informed consent OR having a legally authorized representative (LAR) to provide informed consent for volunteering to undergo research procedure
• Has a clinical, radiographic, or pathological diagnosis of primary or secondary CNS malignancy that has not been treated with radiotherapy

Exclusion Criteria:

• Hypersensitivity to [C-11]-CS1P1 or any of its excipients
• Contraindications to PET, CT or MRI (e.g. certain incompatible electronic medical devices, inability to lie still for extended periods) that make it potentially unsafe for the individual to participate
• Prior cranial radiotherapy
• Severe claustrophobia that would require general anesthesia
• Women who are currently pregnant or breastfeeding
• Any condition that, in the opinion of the Sponsor-Investigator or designee could increase risk to the participant, limit the participant's ability to tolerate the research procedures or interfere with the collection of the data (e.g., advanced renal or liver failure)
• Current or recent (within 12 months prior to screening) participation in research studies involving radioactive agents such that the total research-related radiation dose to the participant in any given year would exceed the limits set forth in the U.S. Code of Federal Regulations (CFR) Title 21 Section 361.1. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=361.1.