People with neuroendocrine cancer typically have imaging scans before and after treatment, including positron emission tomography (PET) scans. The scans are analyzed using a set of criteria that describes how the disease has responded to treatment. The purpose of this study is to establish new criteria for doctors to use when evaluating these PET scans. Researchers are testing whether these new criteria are useful for predicting whether a person's cancer gets better, gets worse, or stays the same. Researchers will also compare these new criteria to the current standard criteria for evaluating imaging scans.

Subjects affected by histologically proven, somatostatin-receptor positive, metastatic or inoperable well-differentiated G1, G2 or G3 neuroendocrine tumors (NETs) candidate to receive PRRT with 177Lu-DOTATATE per standard of care.

Inclusion Criteria:

1. Histologically proven or cytologically confirmed, metastatic or inoperable NETs
2. Measurable disease as defined by RECIST 1.1.
3. Overexpression of somatostatin receptors of the target lesions at somatostatin receptor imaging (68Ga-DOTATATE or 64Cu-DOTATATE PET/CT) with SUV of lesions greater than normal liver at least in 1 metastasis.

Exclusion Criteria:

1. Neuroendocrine Carcinoma), small and large cell type; MIxed Neuroendocrine-Nonneuroendocrine Neoplasm (MiNEN).
2. Presence of somatostatin receptor negative lesions.

Potential research subjects will be identified by a member of the patient's treatment team, the protocol investigator, or research team at Memorial Sloan Kettering (MSK).

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.