This early phase I trial determines where and to what degree the tracer \[68Ga\] Ga-FAPI-04 accumulates in normal and cancer tissues in patients with high grade neuroendocrine cancer. PET is an established imaging technique that utilizes small amounts of radioactivity attached to very minimal amounts of tracer, in the case of this research \[68Ga\] Ga-FAPI-04. Because some cancers take up \[68Ga\] Ga-FAPI-04, it can be seen with PET. CT utilizes x-rays that traverse body from the outside. CT images provide an exact outline of organs and potential inflammatory tissue where it occurs in patient's body.