In addition to identifying where cancer has spread in the body, PET is part of promising new research to help scientists better understand the biology underlying specific cancers and to predict how the disease will respond to specific treatments.
PET involves the use of an imaging device (PET scanner) and an imaging agent called radiotracer that is injected into the patient’s bloodstream. Combining the PET scan with computed tomography (CT) provides both anatomic and molecular information on the area of the body being studied.
Different radiotracers hone in on a specific chemical activity in the body. Most PET scanning today is performed with 18F-fluorodeoxyglucose (FDG), which accumulates in areas where there is a lot of sugar consumption, such as fast growing cancer cells.
But researchers are experimenting with new PET radiotracers, including fluorothymidine (FLT) that may indicate — early in the treatment process — when chemotherapy is working.
Chemotherapy is effective for many breast cancer patients, but not all. Other women respond to one chemotherapy drug, but not another. Currently, the results of systemic therapy can only be determined after a woman completes the therapy — and endures any treatment-related side effects. Studies have shown that tumors that take up less FLT tracer after treatment are more likely to respond to chemotherapy. Several trials are currently underway to validate early findings.
Another PET radiotracer called 16-alpha-[18F]-fluoroestradiol (FES) allows researchers to image the estrogen receptors on cells in the breast. FES PET may allow researchers to better understand why hormonal therapy is not effective in some women with estrogen-positive breast cancer (ER+) — and to predict which patients with ER+ cancer will respond to hormonal therapy.
Other radiotracers are being developed and tested for their ability to image the biologic characteristics of breast cancers, as well as tumor metabolic activity. The ability to image actual therapeutic targets, such as estrogen receptors or human epidermal growth factor receptor-2 (HER-2), will also allow researchers to test the effectiveness of new drugs.