FDG PET/CT and NaF PET/CT imaging quantification of osseous metastatic lesions in patients with metastatic genitourinary (mGU) cancer and their association with survival outcomes.
Authors: Columbres Rod Carlo , Simon Nicholas I. , Chandran Elias , Lei Katherine , Verdini Nicholas Peter , Lin Jeffrey , Vega Andy , Niglio Scot Anthony , Cordes Lisa M. , Ley Lisa , Wang Tzu-fang , Mortazavi Amir , Pal Sumanta Kumar , Knopp Michael V. , Wright Chadwick , Jung Alex , Steinberg Seth M. , Mena Gonzalez Esther , Lindenberg Liza , Apolo Andrea B. 
Published: June 2023

e16573 Background: Identifying osseous lesions and quantifying their response to therapy is challenging. 18F-fluorodeoxyglucose (FDG) and 18F-sodium Fluoride (NaF) PET/CT are both functional imaging modalities with increased sensitivity and specificity for detecting osseous lesions. This study analyzed the association of baseline FDG PET/CT and NaF PET/CT semi-quantitative parameters of bone lesions with or without additional visceral metastasis with survival for patients (pts) with non-prostate mGU malignancies treated on a phase I study with Cabozantinib (Cabo), Nivolumab (Nivo) +/- Ipilimumab (Ipi). Methods: Patients underwent sequential FDG PET/CT and NaF PET/CT scans at baseline. Semi-quantitative imaging parameters were measured including maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) for FDG and fluoride uptake tumor volume (FTV) and total lesion fluoride uptake (TLF) for NaF. Total bone lesion number was captured for all scans. Bone lesion CT characteristics were grouped into 4 categories (0 = normal, 1 = osteolytic, 2 = osteoblastic and 3 = mixed). Semi-quantitative parameters were divided to create two equally sized groups (low vs high) and the association of imaging parameters and survival was determined with Kaplan-Meier curves. Results: We analyzed 40 pts with non-prostate mGU cancers and osseous metastases with or without additional visceral metastasis. Thirty-four (85%) were males; median age was 56 (range 23-81); Histologically, 19 (48%) had urothelial carcinoma, 8 renal carcinoma, 5 testicular, 2 penile cancer, 2 renal medullary, 2 urachal/adenocarcinoma, 1 mucinous and 1 bladder clear cell. Eighteen pts had mixed bone lesion CT characteristic, 8 osteolytic, 4 osteoblastic and 10 normal. A total of 111 osseous lesions were detected on FDG PET/CT while 251 lesions were detected on NaF PET/CT. FDG PET/CT low vs high SUVmax and low vs high TLG were associated with improved OS [25 months(mo) (95% CI: 14.0 – not estimable) vs 8.8 mo (2.9-25.4), p = 0.034], and [25.4mo (17.0 – not estimable) vs 8.8 mo (2.9 -24.9), p = 0.018], respectively. There was no difference in OS for pts with bone only disease compared to pts with bone and visceral disease [21mo (8.4-37.2 vs 14 mo (3.2-25.4), p = 0.12] though there was a difference in PFS [13.4mo (4.8-18.3) vs 4.5 mo (1.7-5.8), p = 0.044]. There were no NaF PET/CT semi-quantitative parameters that were associated with survival outcomes, and CT characterization of osseous lesions was also not found to be associated with survival outcomes. Conclusions: FDG PET/CT semi-quantitative parameters showed potential prognostic capabilities in pts with non-prostate mGU malignancies with bone +/- visceral metastases treated on a phase I study with CaboNivo +/- Ipi. Additional parameters and histologic subsets will be presented.