(A and B) Transaxial CT and fused PET/CT images of primary tumor at baseline. (C and D) Corresponding images after 2 courses of NAC. Source: Journal of Nuclear Medicine

Two recently published PET studies reveal the ways in which molecular imaging can be used to treat difficult cases of breast cancer. The first deals with an imaging agent that targets estrogen receptors (ER) in ER-positive breast cancer patients with formerly inconclusive assessments, and the second highlights the ability of ¹⁸F-FDG to help predict the prognosis for patients undergoing chemotherapy for a very aggressive type of breast cancer. Both studies were published in the February issue of the Journal of Nuclear Medicine.

Conventional imaging and biopsy are not always enough to diagnose and characterize suspected metastatic breast cancers, especially for patients who cannot receive repeated biopsies due to the location of the cancer or other existing illnesses. Approximately 75 percent of breast tumors show ER activity at diagnosis, and that ER expression is an indicator of not only active cancer lesions, but patients’ potential response to therapy as well.

“Whole-body PET with [¹⁸F-FES] provides a unique method to noninvasively obtain molecular information about ER expression,” wrote Geke Hospers, MD, PhD, professor of medical oncology, University Medical Center Groningen, The Netherlands, and colleagues. “Several studies have shown that ¹⁸F-FES PET can reliably detect ER-positive tumor lesions and that ¹⁸F-FES uptake correlates well with immunohistochemical scoring for ER.”

The authors set out to evaluate the value of ¹⁸F-FES using questionnaires directed at referring physicians who requested ¹⁸F-FES PET studies to determine indication, diagnostic value and therapeutic consequences of the procedure.

Results showed that whole-body imaging of ER expression with ¹⁸F-FES PET can be a valuable diagnostic tool. While uptake was variable between all metastases, ¹⁸F-FES PET improved diagnostic understanding in 88 percent of patients and resulted in therapy change in 48 percent of patients. This molecular imaging technique was especially helpful for detecting bone metastases.

“The specificity of the FES-tracer for estrogen receptors makes this technique ideal for aiding physicians working with clinical dilemmas in ER-positive breast cancer patients and could potentially lead to faster diagnoses and earlier implementation of appropriate treatments,” said Hospers.

The second study focused on patients with triple-negative breast cancer receiving chemotherapy before scheduled surgery. David Groheux, MD, of Saint-Louis Hospital in Paris, and colleagues evaluated whether changes in ¹⁸F-FDG tumor uptake could help predict therapy response and prognosis after treatment.

Twenty patients with triple-negative breast cancer underwent PET imaging with ¹⁸F-FDG at the outset of chemotherapy and again after the second cycle of treatment and were evaluated to determine metabolic changes in tumors during therapy. At the point of surgery, six patients showed that their therapy had been completely successful, and 14 were found to have remaining tumors after therapy. Researchers estimated that patients with a less than 42 percent decrease in metabolism of the agent after two cycles of chemotherapy still had some residual cancer after treatment and were therefore at high risk of early relapse.

“If these findings are confirmed by other teams, interim ¹⁸F-FDG-PET/CT could become a major tool for early response assessment of this aggressive cancer, similar to the role ¹⁸F-FDG plays in assessing aggressive lymphomas,” said Groheux. “Also, if these data are confirmed, patients not responding to chemotherapy prior to surgery could be switched to novel treatments that are now being investigated for this specific subtype of breast cancer, which could potentially improve the prognosis for these patients.”

Further research could expand the use of both ¹⁸F-FES and ¹⁸F-FDG for more accurate diagnosis, tumor characterization, therapy monitoring and prognosis for patients with aggressive, complex and challenging breast cancer cases.