This study will evaluate how Gallium-68 Pentixafor is distributed in neuroendocrine tumor patients and if that distribution is consistent through repeated scans. This is an RDRC study - as such, the images obtained for this study cannot be used clinically or shared with treating oncologists.

High grade neuroendocrine tumors often do not express somatostatin (sstr) receptors but often express the CXCR4 receptor. The CXCR4 receptor is a marker of poorly differentiated cells. Pentixafor is a peptide that targets these CXCR4 receptors. By combining it with gallium-68, a radionuclide, pentixafor can then be evaluated as an imaging agent to detect high-grade neuroendocrine tumors.

[68Ga]Pentixafor is a radio-labelled imaging agent used for positron emission tomography (PET). The dose is small, known as a tracer dose. It is designed to capture information about the body and how the body is working without interfering or causing an effect.

The goal of this study is to evaluate how the [68Ga]Pentixafor is distributed through the body after injection and how it is taken up by the organs of the body. The study will also examine if the imaging is reproducible to determine if the PET images show the same uptake of the study drug across different scans.

This study is an RDRC study - the equivalent to a phase 0 study. The [68Ga]Pentixafor has not been shown to target tumors; specificity and sensitivity have not been established. For this reason, images obtained for this study cannot be used clinically or shared with treating oncologists.

Inclusion Criteria:

1. Age ≥ 18 years
2. Histological diagnosis of neuroendocrine tumor (NET).
3. Had a prior 68Ga DOTATATE PET/CT scan (NetSpot) and a CT or MRI with or without contrast performed within 3 months before signing the consent, without interval treatment other than a somatostatin analog.
4. CT or MRI must demonstrate at least one lesion (primary or metastatic) present 1.5 cm or larger in any dimension on cross-sectional imaging (CT or MRI) obtained within 3 months of study enrollment.
5. Results of CXCR4 immunohistochemistry or slides from biopsy of primary tumor or metastatic lesions available for study analysis.
6. Participation in the Iowa Neuroendocrine Tumor Registry.

Exclusion Criteria:

1. Uncontrolled intercurrent illness including, but not limited to ongoing or active infection requiring hospitalization, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
2. Physical limitation that would limit compliance with the study requirements
3. Pregnant or lactating women. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately. A negative pregnancy test will be required for all female subjects with child bearing potential.
4. Planned administration of any NET therapy between scan 1 and 2, except for Somatostatin analog.

Individual participant data will be shared upon request to the study's principal investigator. A signed usage agreement will need to be provided.

After the study has been completed.

Individual participant data will be shared upon request to the study's principal investigator. A signed usage agreement will need to be provided.