PET tracer may predict response to therapy in bone-dominant breast cancer patients

A prospective comparison study of two PET tracers found 18F-FDG could provide valuable measures of activity in bone-dominant (BD) metastatic breast cancer (MBC) patients, while also predicting responses to therapy.

In the study, published online May 10 in the Journal of Nuclear Medicine, authors noted 18F-FDG has predicted time to skeletal-related event (tSRE) and treatment predicted time-to-progression (TTP) in previous research. While, 18F-NaF PET has improved areas related to bone scan and SPECT imaging. Despite this, progress using these tracers has been limited in the clinical setting.

“Response Evaluation Criteria in Solid Tumors (RECIST) criteria specifically exclude bone metastasis as a measurable site for response, and BD MBC patients are often excluded from clinical trials that measure response,” wrote corresponding author Lanell M. Peterson, with the Division of Medical Oncology at the University of Seattle, and colleagues. “This represents a large patient population that could benefit from improved use of systemic therapy, making accurate assessment of BD MBC response an imperative need.”

Researchers imaged 28 patients with 18F-FDG PET and 18F-NaF PET before beginning therapy and then again four months later.

Researchers measured for complete response (CR), partial response (PR), stable disease (SD), progressive disease (PD), tSRE, TTP and overall survival. Modified PET response criteria in solid tumors (mPERCIST) criteria were also used.

“Changes in 18F-FDG PET parameters during therapy are predictive of tSRE and TTP, but not overall survival,” Peterson et al. wrote. “mPERCIST evaluation in bone lesions may be useful in assessing response to therapy and is worthy of evaluation in multicenter, prospective trials. Serial 18F-NaF PET was associated with overall survival but was not useful for predicting TTP or tSRE in BD MBC.”

The authors wrote these results warrant a larger prospective trial of 18F-FDG PET/CT. They also suggested the tracer “could be used as a response endpoint that would increase access of this patient population to clinical trials and promising new therapies.”