An ECOG-ACRIN imaging study solves a long-standing gap in metastatic breast cancer research and care: accurately measuring treatment response in patients with bone metastases

(Press-News.org) A prospective, multicenter cancer clinical trial by the ECOG-ACRIN Cancer Research Group (ECOG-ACRIN) has validated an improved method for predicting treatment benefits in patients with hormone receptor-positive (HR+) metastatic breast cancer that has spread primarily or exclusively to the bones. These patients make up a large portion of individuals who are living with advanced breast cancer—yet are routinely excluded from clinical trials that rely on standard imaging-based assessments (i.e., RECIST 1.1). The study demonstrated that metabolic change assessed by FDG-PET/CT accurately predicted progression-free survival as early as 12 weeks after treatment initiation. 

The study’s co-lead investigator, Jennifer M. Specht, MD, a medical oncologist at the University of Washington and Fred Hutch Cancer Center, presented the results of the FEATURE trial (EA1183, NCT04316117) at the 2025 San Antonio Breast Cancer Symposium. Heather Jacene, MD, a nuclear medicine physician from Brigham and Women’s Hospital and Dana-Farber Cancer Institute, co-led the trial with Dr. Specht.  

“Our study provides the first prospective validation of FDG-PET/CT and PERCIST response criteria in patients presenting with bone-only or bone-dominant metastatic breast cancer,” said Dr. Specht. “This methodology has the potential to inform patients about whether their treatment is working, rather than waiting for late-stage disease progression.” 

Bone is the most common site of breast cancer metastases, and patients with this condition often have more indolent disease than those whose cancer has spread to visceral organs, she said.  

The FEATURE trial sought to overcome two long-standing limitations in research and care by applying readily available clinical tools.   

Dr. Jacene stated, “Standard imaging methods, such as CT, MRI, and bone scans, can detect metastases but do not accurately assess how well systemic therapies are working. The conventional assessment of treatment response in solid tumors, known as RECIST 1.1, classifies bone metastases as non-measurable and non-targetable.”  

FEATURE evaluated FDG-PET/CT, an advanced imaging technique that measures metabolic activity in cancer cells, including bone lesions. The trial utilized the PERCIST criteria to evaluate FDG PET metabolic changes, with a modification to adjust for lower metabolic uptake in bone lesions (mPERCIST). These guidelines are specifically designed for advanced imaging techniques such as PET/CT. Together, these clinical tools have the potential to provide a more sensitive, biologically relevant evaluation of treatment effectiveness.  

The FEATURE trial included 138 patients who underwent FDG-PET/CT imaging before starting treatment and again at 12 weeks. Patients were then scanned at regular intervals with standard imaging and followed for clinical outcomes for a minimum of 3 years and a maximum of 5 years.  

The trial met its primary objective by demonstrating that test results at 12 weeks after therapy initiation could indicate whether patients would continue to do well without their disease worsening. Patients without progressive metabolic disease (PMD) at 12 weeks after treatment initiation had a median progression-free survival of 1.6 years (19.4 months), compared with a mere 3 months in those with PMD. This finding successfully establishes a correlation between 12-week treatment responses and progression-free survival.  

As part of the primary analysis plan, the team evaluated whether FDG-PET/CT modified PERCIST criteria independently predicted PFS. The results indicated that when scans performed at 12 weeks showed no signs of disease progression, the hazard of cancer worsening was approximately 83% lower. This finding is highly statistically significant, underscoring the strong predictive value of early metabolic response. 

“The FEATURE trial shows that FDG-PET/CT with mPERCIST is not only feasible, but clinically meaningful for assessing treatment response in this historically understudied group,” said Dr. Specht. “For the first time, we have a clinically accessible strategy to evaluate how well patients with bone-dominant or bone-only metastatic disease are responding to systemic therapy—with accuracy to guide treatment decisions.”  

Dr. Jacene added, “We now have the data to support that with FDG-PET/CT, we can measure the ‘unmeasurable’.”  

Dr. Specht, Dr. Jacene, and the ECOG-ACRIN research team are calling for continued evaluation of FDG-PET/CT and mPERCIST in clinical trials and for broader integration of metabolic response assessment in patients with bone-only or bone-dominant metastatic breast cancer. 

“If we want to improve outcomes, we need to stop treating bone-only or bone-dominant metastatic breast cancer as unmeasurable,” they emphasized. “This study provides a practical solution—one that can help patients receive the right therapy sooner, and that can finally bring this large patient group into the clinical research landscape.” 

Results of other secondary objectives will be presented when the data are mature. 

This multi-center trial involved investigators and patients at 35 hospitals and cancer centers across the United States and in Ireland. It received support from the National Cancer Institute, one of the US National Institutes of Health, and was accessible through NCI’s National Clinical Trials Network (NCTN) and the NCI Community Oncology Research Program (NCORP).   

About ECOG-ACRIN 

The ECOG-ACRIN Cancer Research Group is a membership-based scientific organization known for advancing precision medicine and biomarker research through its leadership of major national clinical trials that integrate innovative genomic approaches. Nearly 21,000 member researchers and advocates from about 1,400 academic medical centers and community hospitals collaborate across 40 scientific committees to design studies spanning the cancer care spectrum, from early detection to the management of advanced disease. To learn more, visit www.ecog-acrin.org and follow us on X@EAonc, Facebook, LinkedIn, YouTube, and Instagram. 

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