Abstract 90P
Background
In the tumor microenvironment, sarcoma cells and sarcoma-associated fibroblasts frequently show high levels of fibroblast activation protein-a (FAP). This makes it an attractive target for imaging and therapy. The degree of FAP expression and the diagnostic usefulness of 68Ga-FAP inhibitor (FAPI) PET for each sarcoma subtype remain uncertain. We aim to evaluate the diagnostic performance and accuracy of 68Ga-FAPI PET in diverse sarcoma histotypes. We also want to look into the viability of radioligand therapy in this population and determine which subset of patients might benefit the most from it.
Methods
Thus far, this non-randomized phase II study has enrolled six patients with soft tissue sarcomas (STS). The included patients could be at any stage of the disease (localized or advanced) and had received or not received one or more lines of therapy. All patients underwent PET/CT with 68Ga-FAPI-46 in the absence of active treatments, either before starting one or at the time of disease progression. Prior to the the procedure, all of them underwent comprehensive blood tests for kidney and liver function.
Results
Three female and four male STS patients, with a median age of 68.3 years, have been enrolled thus far. Five patients underwent primary tumor resection and required additional lines of chemotherapy in the metastatic scenario. One patient had a recently diagnosed case of localized desmoid fibromatosis. Four of these (solitary fibrous tumor, desmoid fibromatosis, high grade myxoid liposarcoma, and retroperitoneal dedifferentiated liposarcoma) showed positive results. While the polmonary low grade leiomyosarcoma was negative, the patient with retroperitoneal well differentiated liposarcoma displayed unambiguous uptake. The table summarizes the characteristics of the patients. Table: 90P
| Histology | Gender | Age | N°of lesions | Max lesion diam. | Prev. Surgery | Prev. Chemo. | 68Ga-FAPI PET positivity | 68Ga-FAPI PET SUV max |
| RP DDLPS | Male | 79 | >5 | 73x55 mm | Yes | 2 lines | YES | 7.2 |
| MLPS | Male | 45 | >5 | 48x25 mm | Yes | 1 neoadj | YES | 3.2 |
| LG Leiomyosarcoma | Female | 66 | > 5 | 89x46 mm | Yes | 2 lines | NO | NA |
| Desmoid Tumor | Male | 66 | 1 | 120x30x70 mm | No | No | YES | 13.5 |
| RP WDLPS | Male | 78 | 3 | 27 x22 mm | Yes | 2 lines | YES | 13.8 |
| STF | Male | 77 | 2 | 63x46 mm | Yes | No | YES | 11.8 |
Conclusions
Our study's initial findings are promising, showing a high rate of positive regardless of histology.
Clinical trial identification
NCT06136065.
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.