Breast Cancer Screening using PET Scans
PET is an acronym which stands for “Positron Emission Tomography”. Interpreting PET scans is part of a branch of internal or nuclear medicine.
With PET imaging, a radiologist injects a small amount of radioactive dye into the patient and then measures the uptake of the dye as it passes through different parts of the body.
Normally, a PET scan actually scans the whole body and is sometimes used as part of breast cancer staging to check for metastasis of the cancer to other parts of the body. (Scinti scans are also frequently used).
PET scans measure changes in the metabolic rate. So, because cancer cells have a slightly higher metabolic rate than other cells, the PET scan will show ‘hot spots‘ of increased density where malignant cancer masses are likely developing.
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PET scans are useful ‘in between’ breast cancer screening and breast cancer staging
Normally, a PET scan is not used for breast cancer screening. In a way, the use of PET scanning would be for a certain ‘in between‘ situation, when something unusual shows up on a screening mammogram, but there is not yet a confirmation of breast cancer.
Breast cancer specialists may employ PET scans as part of the ‘problem solving‘ process. This is where the doctors try to figure out which other tests, such as biopsies, might be necessary.
So, in many cases PET scans are useful as a means of reassurance that a biopsy was not in fact necessary. Or, if a pseudo-mass appears ‘hot‘ on the PET scan, that might help make the case for a breast tissue biopsy.
PET Scans in the Staging of Breast Cancer
Of course, once there is an official confirmation of a breast cancer diagnosis the staging process begins. Indeed, one of the most essential aspects of the staging process is to determine whether or not the breast cancer has spread to the axillary lymph nodes. Medics will commonly recommend a PET scan for this purpose.
Many oncologists in fact will take a positive PET scan of the axillary region as evidence of metastasis, and not even go ahead with axillary dissections (removing axillary lymph nodes for biospy assessment).
So, the main argument in favor of using breast PET scans in the screening process is to avoid the use of invasive procedures. But PET scans are very expensive and also increase the exposure to radiation.
While PET breast cancer screening has its proponents, the general consensus is that this particular modality is most useful in the staging (and re-staging, where there is recurrence) of breast cancer. In addition the PET scan is also useful in monitoring the effectiveness and response to treatments, especially chemotherapy.
Women who have completed treatment, but remain at high risk for recurrence, might also be good candidates for follow-up PET screening. The use of PET scans to rule out axillary node metastasis of breast cancer is now widely in use.
Use of PET breast scans may increase as a result of genetic-molecular breast cancer research
With research paying a lot of attention to the specific genetic and molecular properties of various types and presentations of breast cancer, we could see the use of PET emerge more strongly as part of the screening process.
Since PET technology monitors metabolic processes at the molecular level, a fine-tuning of the process using dyes engineered to react only to particular molecular charactertiscs may be able to give a clearer identification of a given breast cancer. A PET scan can also assist in predicting cancer behaviour and to help in tailoring the most effective treatment.
Positron Emission Mammography PEM
A new technique, “Positron Emission Mammography” is under discussion in various breast cancer screening studies. Essentially, this technique uses a modified technical apparatus with detectors arranged around the smaller size of the breast, and employs a higher resolution.
On the whole, preliminary studies demonstrate PEM to have a lower rate of false positives than breast MRI. Of course, breast MRI is very useful in detecting the ‘extent‘ of breast tumors and has many positive applications. It is unlikely that PEM will gain broad acceptance, unless it can be shown to reduce costs and give additional time saving and life saving information, not available to the other modalities.
Let’s do a little quiz…
What is a PET scan?
PET stands for Positron Emission Tomography and is an imaging test that allows doctors to check for disease in your body. The scan uses radioactive tracers in special dye.
Specialist radiologists inject these tracers into a vein in your arm. The organs and tissue of the body absorb the radioactive dye. Once the PET scanner highlights these tracers the doctor can see how well your organs and tissues are working.
The PET scan is able to measure:-
- blood flow
- oxygen use
- glucose metabolism (how your body uses sugar)
- and much, much more.
A PET scan is typically an outpatient procedure, meaning that you will be able to go about your day after the test is complete.
Why Perform a PET Scan?
Your doctor may order a PET scan to inspect the blood flow, oxygen intake and metabolism of your organs and tissues. Medics may order PET scans to detect:-
- heart problems
- brain disorders
- problems with the central nervous system.
Unlike other imaging tests, such as CT or MRI scans, a PET scan shows abnormalities within tissues at the cellular level. The PET scan provides your doctor with the best view of complex systemic diseases such as coronary artery disease, brain tumors, memory disorders, and seizures.
When used to detect cancer, the test allows doctors to see how the cancer metabolizes, how it may spread and how well treatments are working.
What are some risks of a PET scan?
While the scan does involve radioactive tracers, the exposure to harmful radiation is minimal. Radiation levels are too low to affect the normal processes of the body.
The risks of the test are minimal in comparison to the beneficial results of diagnosing serious medical conditions. However, the radiation may be unsafe for developing fetuses, so women who are pregnant, think they might be pregnant, or are nursing should not undergo a PET scan.
Other risks of the test include feelings of discomfort if you are claustrophobic or are uncomfortable with needles.
How do I prepare for a PET scan?
Your doctor will provide you with complete instructions about how to prepare for your PET scan.
- Tell your doctor about any medications you are taking. Including whether they are prescription, over-the-counter or supplemental.
- Do not eat anything for up to eight hours before your procedure. You will, however, be able to drink water.
- If you are pregnant, or believe you could be pregnant, tell your doctor because the test may be unsafe for your baby.
- Tell your doctor about any medical conditions you have. For example, diabetics have special instructions for test preparation because fasting beforehand can affect their blood sugar levels.
- You may have to change into a hospital gown.
- You will also need to remove all of your jewellery and/or body piercings because metal can interfere with the testing equipment.
How is a PET scan performed?
Before the scan, medics administer the tracers through an IV in your arm, through a solution you drink, or in a gas you inhale.
Your body needs time to absorb the tracers, so you will wait about an hour before the scan begins. Next, you will undergo the scan.
This involves lying on a narrow table attached to the PET machine, which looks like a giant toilet paper roll. The table glides slowly into the machine so that the scan can be conducted. You will need to lie still during the scan, and the technician will tell you when you need to remain still. The technician may ask you to hold your breath for short periods. You will hear buzzing and clicking noises during the test. When all the necessary images have been recorded, you will slide out of the machine. The test is then complete.
What happens after a PET scan?
After the test, you will be free to go about your day, unless your doctor gives you other instructions. Drink plenty of fluids after the test to help flush the tracers out of your system.
Generally, all tracers will have left your body after two days. Meanwhile, a trained specialist will interpret the PET images and share the information with your doctor. Your doctor will then go over the results with you at a follow-up appointment.
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