As slow disease progression is observed in a subset of mccRCC patients, watchful waiting can be considered, thereby postponing toxicity of systemic treatment. To identify those patients, the IMPACT trial evaluated the role of anti-Carbonic Anhydrase IX antibody 89Zr-girentuximab and 18F-fluorodeoxyglucose (FDG) PET/CT (PET). Here, we report preliminary analyses of a secondary endpoint: comparison of baseline contrast-enhanced(ce)CT, 89Zr-girentuximab and FDG PET to detect metastases.
mccRCC pts with good or intermediate prognosis (according to IMDC) and eligible for watchful waiting were included. Patients underwent 3 scans, i.e. ceCT, 89Zr-girentuximab and 18F-FDG PET. So far, baseline scans of 29 of the 40 pts to be accrued were independently reviewed by 3 experienced readers. Lesions by ceCT were defined positive according to RECIST1.1. For lesions with prominent uptake of 89Zr-girentuximab or 18F-FDG, maximum Standardized Uptake Values (SUVmax) were calculated. Analyses were performed on a lesion level, taking clustering of data within patients and lesions into account.
In total 325 lesions were detected by at least one modality (mean 11(2-33) per pt); ceCT detected 52% (95%CI:45;58), 18F-FDG PET 61% (95%CI:55;67) and 89Zr-girentuximab PET 69% (95%CI:63;74). Differences in lesion detection varied across organ sites(p < 0.001). Lesions were visualized by ceCT and 18F-FDG PET in all pts,whereas 89Zr-girentuximab PET detected lesions in 27 of 29 pts. Compared to ceCT, 89Zr-girentuximab PET visualized additional lesions in all organ sites. Location was strongly related with 89Zr-girentuximab uptake; highest uptake in kidney and adrenal gland tumor (mean SUVmax 63.2 and 70.3, resp) and lowest uptake in lung and lymph nodes (mean SUVmax 10.9 and 15.0, resp). After correction for location, no relation was observed between 89Zr-girentuximab SUVmax and tumor size, as measured by ceCT, and 18F-FDG SUVmax.
89Zr-girentuximab and 18F-FDG PET visualize additional lesions compared to ceCT, however correlation was poor. The addition of 89Zr-girentuximab or 18F-FDG PET might aid in deciding to either delay or start systemic treatment.
Clinical trial identification
Legal entity responsible for the study
Radboud University Medical Center (Radboudumc).
Supported by the Dutch Cancer Society.
Supported by the Dutch Cancer Society
All authors have declared no conflicts of interest.