Tryptophan Metabolism in Human Brain Tumors

Tryptophan Metabolism in Human Brain Tumors

The main purpose of this study is to determine the potential clinical utility of PET imaging using the radiotracer [C-11]alpha-methyl-L-tryptophan in the diagnosis, differentiation and monitoring of various brain tumors, both before and after initial treatment. We will also study mechanisms and clinical significance of abnormal brain tumor tryptophan metabolism using resected tumor tissues.

If you agree to take part in this research study, you will be asked to have:

1. a PET scan, 2. brief clinical questionnaires, and 3. biochemical studies of blood and tumor tissue. You may also have a second PET scan later, if you undergo therapy (such as surgery and/or brain radiation), to determine if there are PET signs of tumor. Your ability to participate in the study will be based, in part, on the results of the magnetic resonance images (MRI) in your medical chart from earlier clinical procedures. Once we receive the results of the PET scan, these will be compared to the MRI in order to help us analyze whether the tryptophan uptake tells us anything about the type of tumor in your brain. It will take about 3 hours to complete the PET scan; this includes the completion of the questionnaires, preparation and scanning. The actual scanning time will be 70 minutes. If you are a female of child-bearing age, we will need a small urine sample from you before starting the PET scanning procedure to make absolutely sure that you do not have unknown pregnancy for which radiation exposure might be harmful.

1. The PET scan will be used to measure the accumulation of the injected radioactive tracer AMT in your brain. To make this measurement more accurate, we will use your clinically obtained MRI scan(s), which was used to diagnose the tumor, to identify the exact location and extent of the tumor. For the PET scan, an intravenous catheter (a small tube placed in your vein) will be inserted for the injection of the AMT for this PET scan. It is the tracer that the PET scanner "sees" when performing the scan. The amount of the tracer, which will be given is very small (5 ml, the volume of a teaspoon), and therefore no side effects are expected from the tracer itself. A second intravenous catheter will be inserted to collect blood samples during the scan; a total of less than 2 teaspoons of blood will be collected. Participants may be sedated (put into sleep with some medicine) if they are unable to remain still for the scanning period.
2. On the day of the PET scan, we will ask you to fill out a brief clinical questionnaire, and also an additional multiple-choice questionnaire to screen for potential mood problems (which often coincide with brain tumors). Participants with a potential speech (comprehension) problem will also be administered a brief speech test. The goal of these tests is to identify various clinical problems that can be associated with brain tumors and affected by abnormal tryptophan metabolism that we measure with the PET scan.
3. If you have surgery to remove the tumor, a portion of the removed tissue will be used for biochemical studies. The doctor will not remove more tissue than needed for your care. The blood (obtained during the PET scanning) and tumor tissue (obtained during surgery) will be processed for analysis and stored in a locked container or freezer in a laboratory. In addition, we will review the clinical pathology report, so that we can correlate your PET results to type and grade of the tumor.

Inclusion Criteria:

1. Clinical and MRI diagnosis of an intracranial lesion suspicious for a brain tumor, including primary and metastatic tumors, or a possible residual or recurrent brain tumor (based on clinical imaging); or history of glioma treatment with chemoradiation, even if no definite progression is found on clinical MRI.
2. Age ≥13 years.

Exclusion Criteria:

1. Severe increased intracranial pressure, status epilepticus, or other symptoms requiring emergency or urgent intervention.
2. Resective surgery within 2 months prior to the PET scan (acute/subacute post-surgical inflammatory changes may cause false positive increases on AMT PET).
3. Positive pregnancy test (because of radiation involved in PET scanning).