In a German single-center phase II trial reported in The Lancet Oncology, Pabst et al found that use of the fibroblast activation protein α (FAP)–directed radiotracer Ga-68–FAPi-46 for positron-emission tomography-computed tomography (PET-CT) has shown promising ability to identify FAP-expressing tumors.
Study Details
The study involved 155 patients enrolled at University Hospital Essen in Germany between December 2021 and February 2024. Patients had at least one measurable tumor lesion (> 1 cm) and confirmed or suspected diagnosis of breast cancer, colorectal cancer, endometrial cancer, esophageal cancer, head and neck cancer, ovarian cancer, pancreatic ductal adenocarcinoma, prostate cancer, thyroid cancer, glioma, hepatocellular carcinoma, lymphoma, multiple myeloma, non–small cell lung cancer, renal cell carcinoma, sarcoma, seminoma, cancer of unknown primary origin, or other tumor types. They had planned or undergone recent surgery or biopsy within 8 weeks before or after enrollment.
PET-CT imaging occurred at a median of 11 minutes after intravenous injection of a median of 145 MBq of Ga-68–FAPi-46. The primary outcome measure was the positive predictive value of Ga-68–FAPi-46 PET for detecting immunohistochemical FAP-positive tumors with histopathological confirmation on a per-patient basis and on the basis of biopsied or resected tumor region; the predefined positive predictive value threshold was at least 75%.
Key Findings
The patient-based positive predictive value of Ga-68–FAPi-46 PET for detecting FAP-positive tumors based on immunohistochemical FAP staining was 90% (95% confidence interval [CI] = 84%–95%).
The region-based positive predictive value was 92% (95% CI = 85%–96%), representing 127 (88%) of 144 patients with histopathological validation.
The most common adverse events of any grade included nausea (18%), fatigue (11%), and constipation (7%); five adverse events, all grade 1 or 2, were considered possibly related to treatment (two cases of nausea and one case each of papulopustular rash, dizziness, and headache). Seven serious adverse events occurred, with none considered related to treatment.
The investigators concluded: “These results confirm the safety and potential of Ga-68–FAPi-46 PET as an imaging biomarker for the detection of FAP-expressing tumors. Further studies are warranted to refine the specificity and define the role of Ga-68–FAPi-46 PET in clinical practice.”
Kim M. Pabst, MD, of West German Cancer Center, German Cancer Consortium and National Center for Tumor Diseases site, University Hospital Essen, Essen, Germany, is the corresponding author for The Lancet Oncology article.
Disclosure: The study was funded by SOFIE Biosciences. For full disclosures of all study authors, visit thelancet.com.
