Physiologic imaging takes pictures of cancer based on how the cancer cells function. Cancer cells grow faster than healthy cells. This rapid growth is shown by physiologic imaging. Most physiologic imaging is currently performed using FDG-PET/CT. This type of test uses a small amount of the radioactive sugar, FDG (fluorodeoxyglucose). Because cancer grows more rapidly than healthy tissue, cancer cells will absorb more of the FDG and the radiation given off by the FDG can be detected by the PET (positron emission tomography) scanner. These images are then compared with CT to show where the cancer is located.
After breast cancer is diagnosed, the lymph nodes in the armpit are tested, to see if the cancer has spread there. Imaging is not accurate, so a biopsy must be done for staging purposes. However, in patients with larger breast cancers, who will receive chemotherapy, FDG-PET/CT is 87% accurate in seeing if breast cancer has spread to the lymph nodes. When the test shows possible spread, biopsy should be done to make sure it’s not a false positive, so that the patient doesn’t get more treatment than is really necessary. With certain types of breast cancer, especially invasive lobular carcinoma (ILC), cancer spread may not be detected by FDG PET/CT. So the test is not as helpful in these patients.
In addition to testing for spread of cancer, FDG-PET/CT can help doctors see if a treatment is going to work for a patient. Patients getting chemotherapy have the test before treatment is started, and again 2 months after. In patients where the chemotherapy works, the tumor lights up less after two months. This can show up on the test, even if the tumor doesn’t shrink. FDG-PET/CT is better at detecting breast cancer than usual imaging and so if it is negative, the patient probably has no disease. Some other drugs, which are still being researched, look like they’ll give us this information faster, which will help doctors decide whether to keep going with treatment or change it before the cancer gets worse, if it’s not working. FDG-PET/CT is also better at seeing if cancer has spread to the bones, than other tests.
The future of functional imaging includes the development of other radioactive materials besides FDG, for use with specific types of cancers. These should improve the ability to see if cancer has spread and test whether treatment is working better than FDG-PET/CT.
Physiologic, or functional, imaging is better than older tests in detection and staging of breast cancer, as well as testing whether treatment is working. Ongoing research will lead to better patient care.