Inclusion Criteria:
* Age ≥18 years.
* Targeted lesion (tumor) is at least 1 cm in diameter as shown by clinical imaging.
* Patient is able to lie in the PET/CT scanner for at least 70 minutes while undergoing scanning.
* Women of childbearing potential must not be pregnant or breastfeeding.
* Recent anatomic imaging with visible disease (tumor) for comparison with the PET/CT. .
* Physical exam within 28 days of PET imaging, CBC and Multiphasic (including electrolytes, BUN, creatinine, total bilirubin, AST and ALT) within 14 days.
* Patients must sign an informed consent indicating that they are aware of the investigational nature of this study.
Inclusion Criteria Specific for Intracranial Tumors
\- Clinical and MRI diagnosis of an intracranial lesion suspicious for a brain tumor, including gliomas or metastatic brain tumors; primary, residual, or recurrent brain tumors (judged by clinical imaging) will qualify.
Inclusion Criteria Specific for Extracranial Neuroendocrine Tumors:
* Histopathologically confirmed, well-differentiated metastatic neuroendocrine tumor.
* ECOG performance status of 2 or better.
* Patients receiving stable-dose somatostatin analogs (SSAs, long-acting release \[LAR\], depot) for \>3 months before enrollment may be enrolled on the study, but such treatment is not required.
Inclusion Criteria specific for Extracranial Primary Breast tumors:
* Clinical and radiological diagnosis of a breast cancer
* ECOG performance status of 2 or better.
Inclusion Criteria specific for Rectal tumors:
* Histologically confirmed colorectal cancer, which is located in the rectum.
* ECOG performance status of 2 or better.
Exclusion Criteria:
* Patients who are pregnant or lactating are excluded.
Exclusion Criteria Specific for Intracranial Tumors:
* Severe increased intracranial pressure, status epilepticus, or other symptoms requiring emergency or urgent intervention.
* Tumor surgery or radiation within 1 month prior to the PET scan
Exclusion Criteria Specific for Extracranial Neuroendocrine Tumors:
* Tumor-directed therapy within 3 months to the area of planned imaging.
* Ongoing treatment with a targeted agent (e.g., sunitinib or everolimus) or receiving cytotoxic chemotherapy (e.g., capecitabine or temozolomide).
* Use of telotristat ethyl (a tryptophan-hydroxylase inhibitor) within one month.
Exclusion Criteria for Extracranial Primary Breast tumors:
-Recent (within 1 month) tumor resection or radio-chemotherapy (acute/subacute post-treatment inflammatory changes may cause false positive increases on PET).
Exclusion Criteria for Rectal tumors:
-Active inflammatory bowel disease (Crohn's or Ulcerative colitis) involving the rectum.
