Cancer in Women: The Promise for Personalized Treatment
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Whether it is for breast cancer or ovarian cancer, molecular imaging allows for an evaluation of the extent of the disease as well as patient response to treatment. PET/CT has proven itself an effective imaging choice for staging potential sites of disease and for evaluating and monitoring tumor response to therapy. In the U.S., however, availability and cost/reimbursement play a role in determining widespread use across all indications of women’s cancers. Since 2006, Medicare has only covered patients with cervical and ovarian cancers if they were enrolled in the U.S. National Oncologic PET Registry (NOPR).
Since cancers have a higher energy requirement and therefore accumulate molecular imaging tracers such as fluorodeoxyglucose (FDG) at a greater rate than normal tissue, clinicians can obtain valuable information about tumor activity, says Michael O’Connor, PhD, nuclear medicine at the Mayo Clinic.
The main indications for molecular imaging of women’s cancers are in breast cancer staging, re-staging and therapy response in all risk categories. Cervical cancer staging and ovarian cancer are covered only if referred under NOPR, according to Todd Blodgett, MD, chief of cancer imaging at the University of Pennsylvania Medical Center in Pittsburgh.
While mammography is still king for breast cancer detection and diagnosis, with or without ultrasound or biopsy, PET/CT imaging helps to determine the extent of the breast cancer at the time of staging, to identify liver or osseous metastases, potentially altering treatment options and decisions, says Lale Kostakoglu, MD, MPH, director of PET/CT Oncology and Research at Mount Sinai School of Medicine in New York City.
In patients with cervical cancer, PET/CT imaging is appropriate when the patient is first diagnosed, since it has a potential to change staging by identifying otherwise undetected metastases in lymph nodes or in distant sites. PET/CT also is very effective in patients with clinical suspicion of recurrent disease.
For cervical cancer, PET/CT is now the routine and standard test after initial staging, at the end of curative therapy and in routine follow up, says Perry W. Grigsby, MD, professor of radiation oncology, nuclear medicine and gynecologic oncology at the Mallinckrodt Institute of Radiology in St. Louis. In these cases, PET/CT can help refine areas for inclusion in a radiation therapy field or it can establish the stage of the disease or detect distant metastases.
Utilizing PET/CT for cervical and ovarian cancers, para-aortic lymph node metastases can be more accurately detected with the capability of PET/CT distinguishing blood vessels from adjacent lymph nodes, Kostakoglu says. It is beneficial for patients with a history of ovarian cancer to detect recurrent disease, but coverage issues are yet to be resolved.
“The overall sensitivity and specificity of PET/CT is higher than any other test and more likely to show the tumor sites and demonstrate their location compared to other imaging modalities such as CT or MRI,” Grigsby notes.
However, FDG’s inherent problem is that its uptake in physiological and benign processes allows for some false-positive results; additionally, some tumors do not uptake FDG, generating false negatives. “FDG is not an ideal radiotracer,” says Kostakoglu, adding that the industry needs more specific radiotracers for targeted imaging in oncology.
New biomarkers in development could offer more information about cancer cells and offer improvements in therapeutic monitoring, filling the gap left by FDG. For example, 18F-FLT (fluorothymidine), which several studies indicate is more effective at marking tumor growth than FDG, is less effective for tumor staging due to a lower uptake than that of FDG. In the future, an FLT-PET scan could provide necessary data for monitoring treatment response.
Grigsby notes that PET/CT is currently used to define radiation therapy planning, although it could help routinely monitor and evaluate tumor shrinkage, allowing for more adaptive radiation therapy planning and treatment.
“In the future, we are going to do more boutique imaging, not the one-size-fits-all model like with FDG,” says Kostakoglu. “One has to have access to a sufficient therapeutic armamentarium to use multimodality imaging for patient management changes.”