Targeted radiation shows promise for rare solitary fibrous tumors

A novel targeted radiation approach for a rare form of malignant tumor-the solitary fibrous tumor (SFT)-has shown significant success, achieving a near-complete response in three patients. The therapy significantly reduced cancer activity and provided symptom relief, underscoring its potential as a viable treatment option. This research was published in the September issue of The Journal of Nuclear Medicine.

SFT is a rare type of soft tissue tumor with few treatment options available. Although most SFTs are classified as benign with minimal risk of recurrence, about 15 to 20 percent are malignant, and those considered benign have the potential for malignant transformation. For patients with malignant disease, treatment options are scarce, and outcomes are often poor.

In several sarcomas, particularly SFT, fibroblast activation protein (FAP) is highly expressed on the surface of tumor cells and surrounding fibroblasts. We sought to deliver radiation therapy directly to the FAP target with the novel radioligand therapy, ⁹⁰Y-FAPI-46."

Helena Lanzafame, MD, researcher, Department of Nuclear Medicine, University Hospital Essen, Germany

The study included three patients who had already tried multiple standard therapies without success. Molecular analysis of their tumor tissues revealed remarkably high levels of the FAP protein, confirmed with advanced FAPI-46 PET imaging. Patients received four cycles of ⁹⁰Y-FAPI-46 therapy and their treatment response was evaluated with ¹⁸F-FDG and ⁶⁸Ga-FAPI-46 PET/CT.

Imaging revealed that all patients experienced tumor shrinkage or disease stabilization, as well as significant relief from symptoms, such as severe fatigue and abdominal pain. In addition, no serious side effects were observed among the patients.

"This is the first time we have seen such strong and deep responses in advanced SFT using this precision radiation approach," noted Rainer Hamacher, MD, lead oncologist in the Department of Medical Oncology, Sarcoma Center, West German Cancer Center at University Hospital Essen. "Our findings suggest that screening for FAP expression could help identify patients most likely to benefit from this novel therapy."

The team emphasizes that these are early results from a small number of carefully selected patients. Larger prospective clinical trials are needed to confirm the therapy s safety and effectiveness, and to understand how best to integrate it into existing treatment strategies.